What is malware? Everything you need to know about viruses, trojans and malicious software

Cyber attacks and malware are one of the biggest threats on the internet. Learn about the different types of malware – and how to avoid falling victim to attacks.





What is malware?

Malware is shorthand for ‘malicious software’. It is software developed by cyber attackers with the intention of gaining access or causing damage to a computer or network, often while the victim remains oblivious to the fact there’s been a compromise. A common alternative description of malware is ‘computer virus’ – although are big differences between these types malicious programs.

What was the first computer virus?

The origins of the first computer virus is hotly debated: for some, the first instance of a computer virus – software which move from host to host without the input from an active user – was Creeper, which first appeared in the early 1970s, ten years before the actual term ‘computer virus’ was coined by American computer scientist Professor Leonard M. Adleman.

Creeper ran on the Tenex operating system used throughout ARPANET — the Advanced Research Projects Agency Network — and jumped from one system to another, displaying a message of “I’M THE CREEPER : CATCH ME IF YOU CAN’ on infected machines, before transferring itself to another machine. For the most part, when it found a new machine, it removed itself from the previous computer, meaning it wasn’t capable of spreading to multiple computers at once.

While Creeper wasn’t created for malicious purposes or performing any activity beyond causing mild annoyance, it was arguably the first example of software operating in this way.

Shortly afterwards, a new form of software was created to operate in a similar way – but with the aim of removing Creeper. It was called Reaper.

Alternatively, some believe the title of the first computer virus should go to one called Brain, because unlike Creeper it could self-replicate itself without the need to remove itself from a previous system first – something which many forms of malicious code now do.

The Morris Worm

The Morris Worm holds the notorious distinction of the first computer worm to gain mainstream media attention – because within hours of being connected to the early internet, it had infected thousands of computers. The damage of the lost productivity estimated to have cost between $100,000 and $10,000,000.

Like Brain and Creeper before it, the Morris worm isn’t classed as malware because it is another example of an experiment gone wrong.

The software was designed to try to find out the size of the burgeoning internet with a series of scans in 1988, but mistakes in the code led to it running unintended denial of service operations – sometimes multiple times on the same machine, rendering some computers so slow they became useless.

As a result of the Morris Worm, the internet was briefly segmented for several days in order to prevent further spread and clean up networks.

What is the history of malware?

While Creeper, Brain and Morris are early examples of viruses, they were never malware in the truest sense.

Malware and the malicious code behind it is designed specifically to cause damage and problems on computer systems, while those described above found themselves causing issues by accident – although the results were still damaging.

With the birth of the web and the ability to connect to computers around the globe, the early 90s saw internet businesses take off as people looked to provide goods and services using this new technology.

However, as with any other form of new technology, there were those who looked to abuse it for the purposes of making money – or in many cases, just to cause trouble .

In addition to being able to spread via discs – both floppy and CD-Rom varieties – the increased proliferation of personal email allowed attackers to spread malware and viruses via email attachments – especially potent against those without any sort of malware protection.

Various forms of malicious software caused trouble for the computer users of the 1990s, performing actions ranging from deleting data and corrupting hard drives, to just annoying victims by playing sounds or putting ridiculous messages on their machines.

Many can now be viewed – in safe mode with the actual malware removed – at the Malware Museum on the Internet Archive.

Some of the attacks may have looked simple, but it was these which laid down the foundations for malware as we know it today – and all the damage it has caused around the world.


Casino Disk Destroyer – a form of malware in the 90s – made victims play a game of chance before it destroyed content on the disk.

Image: Internet Archive


What are the different types of malware?

Like traditional software, malware has evolved over the years and comes equipped with different functions depending on the goals of the developer

Malware authors will sometimes combine the features of different forms of malware to make an attack more potent – such as using ransomware as a distraction to destroy evidence of a trojan attack.

What is a computer virus?

At its core, a computer virus is a form of software or code which is in able to copy itself onto computers. The name has become associated with additionally performing malicious tasks, such as corrupting or destroying data.

While malicious software has evolved to become far more diverse than just computer viruses – there are still some forms of traditional viruses – like the 15 year old Conficker worm – which can still cause problems for older systems. Malware, on the other hand is designed to provide the attackers with many more malicious tools.

What is trojan malware?

One of the most common forms of malware – the Trojan horse – is a form of malicious software which often disguises itself as a legitimate tool which tricks the user into installing it so it can carry out its malicious goals.

Its name of course comes from the tale of ancient Troy, with the Greeks hidden inside a giant wooden horse which they claimed was a gift to the city of Troy. Once the horse was inside the city walls, the a small team Greeks emerged from inside the giant wooden horse and took the city.


Just as the Greeks used a Trojan Horse to trick Troy into letting troops into the city, Trojan malware disguises itself in order to infiltrate a system.

Image: Getty


Trojan malware operates in much the same way, in that it sneaks into your system – often disguised as a legitimate tool like an update or a Flash download – then once inside your system and begins its attacks.

Once installed the system, depending on its capabilities a Trojan can then potentially access and capture everything – logins and passwords, keystrokes, screenshots, system information, banking details and more – and secretly send it all to the attackers. Sometimes a Trojan can even allow attackers to modify data or turn off anti-malware protection.

The power of Trojan horses makes it a useful tool for everyone from solo hackers, to criminal gangs to state-sponsored operations engaging in full-scale espionage.

What is spyware?

Spyware is software which monitors the actions that are carried out on a PC and other device. That might include web browsing history, apps used or messages sent. Spyware might be arrive as a trojan malware or may be downloaded onto device in other ways.

For example, someone downloading a toolbar for their web browser may find it comes packed with spyware for the purposes of monitoring their internet activity and computer use, or malicious adverts can secretly drop the code onto a computer via a drive-by download.

In some cases, spyware is actively sold as software, designed for purposes such as parents monitoring their child’s internet use and is designed to explicitly be ignored by antivirus and security software. However, there are various instances of such tools being used by employers to spy on the activity of employees and people using spyware to spy on their spouses.

What is ransomware?

While some forms of malware rely on being subtle and remaining hidden for as long as possible, that isn’t the case for ransomware.

Often delivered via a malicious attachment or link in a phishing email, ransomware encrypts the infected system, locking the user out until they pay a ransom – delivered in bitcoin or other cryptocurrency in order to get them back.

It might sound simple, but ransomware works: cybercriminals pocketed over $1bn from ransomware attacks during 2016 alone and a Europol report describes it as having “eclipsed” most other global cybercriminal threats in 2017.


Ransomware demands a payment in return for returning encrypted files.

Image: Malwarebytes

What is wiper malware?

Wiper malware has one simple goal: to completely destroy or erase all data from the targeted computer or network. The wiping could take place after the attackers have secretly removed target data from the network for themselves, or it could could be launched with the pure intention of sabotaging the target.

One of the first major forms of wiper malware was Shamoon, which targeted Saudi energy companies with the aim of stealing data then wiping it from the infected machine. More recent instances of wiper attacks include StoneDrill and Mamba, the latter of which doesn’t just delete files, but renders the hard driver unusable.

One of the most high profile wipers of recent times was Petya ransomware. The malware was initially thought to be ransomware, however, researchers found that not only was there no way for victims retrieve their data via paying the ransom, but also that the goal of Petya was to irrecoverably destroy data.

What is a computer worm?

A worm is a form of malware which is designed to spread itself from system to system without the actions by the users of those systems.

Worms often exploit vulnerabilities in operating systems or software, but are also capable of distributing themselves via email attachments in cases where the worm can gain access to the contact book on an infected machine.

It might seem like a basic concept, but worms are some of the most successful and long-lived forms of malware out there. The 15 year old SQL slammer worm is still causing issues by powering DDoS attacks, while the 10 year old Conficker worm still ranks among the most common cyber infections.

Last year’s Wannacry ransomware outbreak infected over 300,000 computers around the world – something it did thanks to the success of worm capabilities which helped it quickly spread through infected networks and onto unpatched systems.

What is adware?

The ultimate goal of many cybercriminals is to make money – and for some, adware is just the way to do. Adware does exactly what it says on the tin – it’s designed to maliciously push adverts onto the user, often in such a way that the only way to get rid of them is to click through to the advert. For the cybercriminals, each click brings about additional revenue.

In most cases, the malicious adverts aren’t there to steal data from the victim or cause damage to the device, just sufficiently annoy the user into repeatedly clicking on pop-up windows. However, in the case of mobile devices, this can easily lead to extreme battery drain or render the device unusable due to the influx of pop-up windows taking up the whole screen.


Adware displays intrusive pop-up adverts which won’t disappear until they’re clicked on.

Image: iStock


What is a botnet?

A botnet – short for ‘robot network’ involves cybercriminals using malware to secretly hijack a network of machines in numbers which can range from a handful to millions of compromised devices. While is is not malware in itself these networks are usually build be infecting vulnerable devices.

Each of the machines falls under the control of a single attacking operation, which can remotely issue commands to all of the infected machines from a single point.

By issuing commands to all of the infected computers in the zombie network, attackers can carried out coordinated large-scale campaigns, including DDoS attacks, which leverage the power of the army of devices to flood a victim with traffic, overwhelming their website or service to such an extent it goes offline.

Other common attacks carried out by botnets include spam email attachment campaigns – which can also be used to recruit more machines into the network – attempts to steal financial data, while smaller botnets have also been used in attempts to compromise specific targets.

Botnets are designed to stay quiet to ensure the user is completely oblivious that their machine is under the control of an attacker.

As more devices become connected to the internet, more devices are becoming targets for botnets. The infamous Mirai botnet – which slowed down internet services in late 2016 – was partially powered by Internet of Things devices which could easily be roped into the network thanks to their inherently poor security and lack of malware removals tools.

What is a cryptocurrency miner malware?

The high profile of the rise of bitcoin has helped push cryptocurrency into the public eye. In many instances, people aren’t even buying it, but are dedicating a portion of the computing power of their computer network or website to mine for it.

While there are plenty of instances of internet users actively engaging in this activity on their terms – it’s so popular the demand has helped to push up the price of PC gaming graphics cards – cryptocurrency mining is also being abused by cyber attackers.

There’s nothing underhand or illegal about cryptocurrency mining in itself, but in order to acquire as much currency – be it bitcoin, Monero, Etherium or something else – some cybercriminals are using malware to secretly capture PCs and put them to work in a botnet, all without the victim being aware their PC has been compromised.

One of the largest cybercriminal cryptocurrency networks, the Smominru botnet, is thought to consist of over 500,000 systems and to have made its operators at least $3.6 million dollars.

Typically, a cryptocurrency miner will deliver malicious code to a target machine with the goal of taking advantage of the computer’s processing power to run mining operations in the background.

The problem for the user of the infected system is that their system can be slowed down to almost a complete stop by the miner using big chunks of its processing power – which to the victim looks as if it is happening for no reason.


The rise of cryptocurrency has led to a rise in criminals using malware to mine it via compromised systems.

Image: iStock


PC and Window servers can be used for cryptocurrency mining, but Internet of Things devices are also popular targets for compromising for the purposes of illicitly acquiring funds. The lack of security and inherently connected nature of many IoT devices makes them attractive targets for cryptocurrency miners – especially as the device in question is likely to have been installed perhaps even forgotten about.

Analysis by Cisco Talos suggests a single system compromised with a cryptocurrency miner could make 0.28 Monero a day. It might sound like a tiny amount, but an enslaved network of 2000 system could add the funds up to $568 per day – or over $200,000 a year.

How is malware delivered?

In the past, before the pervasive spread of the World Wide Web, malware and viruses would need to be manually, physically, delivered, via floppy disc or CD Rom.

In many cases, malware is still delivered by using an external device, although nowadays it is most likely to be delivered by a flash drive or USB stick. There are instances of USB sticks being left in car parks outside targeted organizations, in the hope that someone picks one up out of curiosity and plugs it into a computer connected to the network.

However, more common now is malware that is delivered in a phishing email with payloads distributed as an email attachment.

The quality of the spam email attempt and vary widely – some efforts to deliver malware will involve the attackers using minimal effort, perhaps even sending an email containing nothing but a randomly named attachment.

In this instance, the attackers are hoping to chance on someone naive enough to just go ahead on click on email attachments or links without thinking about it – and that they don’t have any sort of malware protection installed.

A slightly more sophisticated form of delivering malware via a phishing email is when attackers send large swathes of messages, claiming a user has won a contest, needs to check their online bank account, missed a delivery, needs to pay taxes or even is required to attend court – and various other messages which upon first viewing may draw the target to instantly react.

For example, if the message has an attachment explaining (falsely) why you’re being summoned to court, the user may click on it due to the shock, opening the email attachment – or clicking a link – to get more information. This activates the malware, with the likes of ransomware and trojans often delivered in this way.

If the attackers have a specific target in mind, the phishing email can be specifically tailored to lure in people within one organization, or even just an individual. It’s this means of delivering malware which is often associated with the most sophisticated malware campaigns.

However, there are many other ways for malware to spread that do not require action by the end user – through networks and through other software vulnerabilities.

What is fileless malware?

As traditional malware attacks are slowly being slowed by prevention tactics including the use of robust anti-virus or anti-malware system, and users becoming cautious of unexpected emails and strange attachments, attackers are being forced to find other ways to drop their malicious payloads.

One increasingly common means of this is via the use of fileless malware. Rather than relying on a traditional method of compromise like downloading and executing malicious files on a computer – which can often be detected by anti-virus software solutions – the attacks are delivered in a different way.

Instead of requiring execution from a dropped file, fileless malware attacks rely on leveraging zero-day exploits or launching scripts from memory, techniques which can be used to infect endpoints without leaving a tell-tale trail behind.

This is achieved because the attacks uses a system’s own trusted system files and services to obtain access to devices and launch nefarious activity – all while remaining undetected because anti-virus doesn’t register wrongdoing.

Exploiting the infrastructure of the system in this way allows the attackers to create hidden files and folders or create scripts they can use to compromise systems, connect to networks and eventually command and control servers, providing a means of stealthily conducting activity.

The very nature of fileless malware means not only is it difficult to detect, but difficult to protect against by some forms of antivirus software. But ensuring that systems are patched, up to date and restricted users from adopting admin privileges can help.

Do only Windows PCs get malware?

There was a time when many naively believed that it was only Microsoft Windows systems which could fall victim to malware. After all, malware and viruses had concentrated on these, the most common computer systems, while those which used other operating systems were free of its grasp. But while malware still remains a challenge for Windows systems – especially those running older, even obsolete versions of the OS – malware is far from exclusive to Microsoft PCs

Mac malware

For many years, a myth persisted that Macs were completely immune to malicious infections. Over the course of the 90s there were some forms of malware which did infect Macs, despite primarily being designed for Windows systems. The likes of Concept and Laroux were about to infect Macs using Microsoft office programs.

However, by the mid-00s, attackers had started building forms of malware specifically designed to target Apple Macs and now, while Windows machines bare the brunt of computer and laptop based malware attacks, Macs are now regular targets for cybercrime.

It’s now normal for Backdoors trojans, compromised software downloads and ransomware attacks targeting Mac systems to be uncovered by cybersecurity researchers.


MacRansom is a form of ransomware which targets Macs.

Image: Fortinet


What is mobile malware?

The rise of smartphones and tablets over the last decade has fundamentally changed our relationship with the internet and technology. But like any form of new technology, criminals soon realized that they could exploit smartphones for their own illicit gain – and these mobile devices not only contain vast amounts of personal information, and can even allow hackers to monitor out location.

If there’s a type of malware which can infect computers – be it a trojan, ransomware, or pop-up adware – then criminals have been working on built from the ground up forms of malware which can carry out the same tasks on smartphones.

The amount of data carried on mobile devices makes them an even more valuable target for hackers, particularly if a sophisticated hacking group, or a state-backed espionage operation is looking to compromise a particular target for the purposes of spying.

The inherent abilities of a smartphone mean its ultimately possible, with the use of the right malware, for those groups to physically locate targets or even listen into conversations and take photos of them using the microphone and camera capabilities built into phones.

Unfortunately, many people still don’t realize their mobile phone is something which can fall victim to cyber-attacks – although they can be protected by good user practice and mobile antivirus software.

What is Android malware?

Android phones with suffer the majority of malware attacks on smartphones, with Google’s larger share of the mobile market and the open nature of the ecosystem making it an attractive target for cybercriminals.

Attackers can infect their targets by tricking them into downloading malicious applications from third-party stores and malware has often found its way into the official Google Play application market place.

These malicious apps are often designed to look like original useful tools or games, or in some cases, mimic legitimate apps outright – as demonstrated by a fake version of WhatsApp which was downloaded over a million times.

However, while the Google Play store has been used by hackers to distribute Android malware, more sophisticated campaigns will socially engineer selected targets into downloading malware for the purposes of espionage onto their device.


Android malware is known to pose as legitimate apps inside the Play Store – this one is disguised as a cleaner which tells the user they need to download an additional malicious update. Image: ESET


Can my iPhone become infected by malware?

When it comes to iPhone, the ecosystem is much more heavily protected against malware due to Apple’s closed garden approach to applications.

However, while malware on iPhones is rare, it isn’t an unknown entity – hacking gangs have found ways to compromise the devices of selected targets in espionage campaigns, such as those who exploited the Trident vulnerabilities to install Pegasus spyware to spy on human rights activists in the Middle East.

What is Internet of Things malware?

As the rise of malware on mobile devices has demonstrated, if something is connected to the internet, it’s a potential avenue of cyber-attacks.

So, while the rise of Internet of Things connected devices has brought a number of benefits to users – in industry, the workplace and at home – it too has opened doors for new cyber criminal schemes.

The rush to jump on the IoT bandwagon means that some devices are rushed out with little thought put into cyber security, meaning it remains relatively simple for hackers to infect connected devices, ranging from industrial control systems, to household products to even children’s toys.

One of the most common means in which the insecurity of IoT devices is exploited is with malware attacks which secretly infect products and rope them into a botnet.

Devices like routers, smart lighting systems, VCRs, and surveillance cameras can all easily become infected and the eventual damage can be spectacular – as demonstrated by the online chaos caused by the Mirai botnet DDoS attack.

The network of Mirai infected devices consisted largely of IoT products and was so powerful, it brought large swathes of the internet grinding to a halt, slowing down or outright preventing access to a number of popular services.

While devices infected with Mirai continued to operate as normal, that wasn’t the case for those who found their IoT products infected with BrickerBot, a form of IoT malware that resulted in Homeland Security’s Cyber Emergency Response Team (CERT) issuing new warnings. Devices infected with BrickerBot have their storage corrupted, leading them completely unusable and irrecoverable.

Just like mobile phones can be turned into surveillance devices by hackers, the same can be said of internet connected cameras in the home. There has already been a number of instances where IoT camera security has been found to be so basic that malware has infected large numbers of devices.

Unlike mobile phones, IoT devices are often plugged in and forgotten about, with the risk that the IoT camera you set up could become easily accessible to outsiders – who could potentially use it to spy on your actions, be it in your workplace, or in your home.

Such is the extent of the security worry with the IoT, police have warned about the threats posed by connected devices, while government bodies are working towards ways of legislating IoT devices sooner rather than later so we’re not left with a toxic legacy of billions of devices which can easily be infected with malware.


Everyday objects are increasingly being connected to the Internet of Things – and they’re an attractive target for malware.

Image: iStock


Malware as took for international cyberwarfare

With malware’s offensive capabilities evident, it’s no wonder it has become a common tool in the murky world of international espionage and cyber warfare.

It’s especially useful for those involved in the game of geopolitics because currently, unlike the case with conventional weapons, as yet there are no rules or agreements detailing who can and can’t be targeted by cyber weapons.

That attribution of attacks remains so difficult also makes cyber espionage a crucial tool for nation-states who want to keep their activities under wraps.

Stuxnet is generally regarded as the first instance of malware designed to spy on and subvert industrial systems and in 2010 it infiltrated Iran’s nuclear program, infecting uranium centrifuges and irreparably damaging systems. The attack slowed down Iran’s nuclear ambitions for years.

While no state has officially taken credit for the attacks, it’s believed Stuxnet was the work of US and Israeli cyber forces.

Since that first instance of publicly reported malware attacks by nation states, cyber warfare has become a tool used by governments around the world. It’s widely suspected that nation-state actors were behind attacks against a Ukrainian power plant, but it isn’t just physical systems and infrastructure which are targets for cyber warfare.

Meanwhile, actors on all sides of diplomatic divides continue to undertake cyber espionage campaigns against potentially useful targets.

How do you protect against malware?

Some of the most basic cyber security practices can go a long way to protecting systems – and their users – from falling victim to malware.

Simply ensuring software is patched and up to date and all operating system updates are applied as quickly as possible after they’re released will help protect users from falling victim to attacks using known exploits.

Time and again, delays in patching has led to organization’s falling victims to cyber-attacks which could’ve been prevented if patches had been applied as soon as they were released.

One of the reasons the UK’s National Health Service was so badly impacted by the WannaCry outbreak was because, despite warnings that they should be applied, vast swathes of systems hadn’t been patched weeks after a security update for protecting against the EternalBlue exploit was available.

It’s also common for cyber espionage campaigns to leverage exploits for which fixes have long existed and still successfully compromise targets – because nobody bothered to apply the patches. The lesson to be learned here is that sometimes it might seem time-consuming and inconvenient to apply patches – especially across a whole network – but it can prove to be an effective barrier against malware.

Installing some form of cyber security software is also a useful means of protecting against many forms of attack. Many vendors will update their programs on a weekly or even daily basis, providing as much protection as possible from malware, should something attempt to break into the system.

For example, visitors to watering hole sites should be protected from attacks, while suspicious or dangerous files received via email can be quarantined.

User training should also be offered in order to ensure everyone using your network is aware of the cyber threats they could face on the internet.

Teaching users about the dangers of phishing emails or to be wary of what they download and click can help prevent threats from getting to the point of even being downloaded. Users take a lot of criticism from some as a weakness in cyber security, but they can also form the first line of defense against malware attacks.