What is a Computer Worm and How Do You Prevent Infection?

After affecting one device, a computer worm goes on to the next one
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A Quick Guide: What is a Computer Worm and How Do You Prevent Them?

Computer worms are a type of malware that’s able to replicate itself across computers, operating systems, and entire networks without human interaction. A computer worm must first be downloaded onto a device, typically through clicking a phishing email link, downloading a malicious attachment, or falling victim to a social engineering attack. Once the breach has occurred, the worm is able to spread all by itself across connected devices and networks.

There are many different types of worms, some more dangerous than others:

  1. Payload worms (carry malware)
  2. Cryptoworms (ex. WannaCry ransomware)
  3. Bot worms (create botnets)
  4. Email worms (through spam emails)
  5. Instant messaging worms (via social media)
  6. Internet worms (through unsecured websites)
  7. File-sharing worms (through torrenting)

Though computer worms aren’t technically considered viruses, premium antivirus software programs provide protection against them. For the first line of defense against this malware, check out our top 5 antivirus programs.

Want to learn more about computer worms and how to prevent them? Read the full article below.

Computer worms are a particularly persistent, disruptive, and hard-to-detect form of malware. Once a computer worm has wriggled its way onto a computer, it’s able to replicate and spread through servers, networks, and other devices. Worms do this without the victims being aware it’s happening.

Some worms are merely a nuisance, as they eat up bandwidth and memory on devices, slowing down performance and connections. Others are extremely malicious and can have devastating consequences for businesses and individuals alike.

Because they self-copy and spread automatically, computer worms are different from viruses and other forms of malware. In this article, we’ll explain what exactly that difference is, how computer worms work, and how you can protect yourself from them.

How Do Computer Worms Spread?

Like many cyberattacks and malware infections, hackers and threat actors often use phishing techniques or social engineering tactics to get a computer worm onto someone’s computer. Once that initial attack is done, the computer worm starts its malicious journey all on its own.

When a computer or network is infected with a worm, the worm will automatically begin looking for other devices to latch onto. So when you connect your infected laptop to your home Wi-Fi or Local Area Network (LAN), the computer worm immediately tries to infect anything connected to that same network. This could include laptops, smartphones, tablets, servers, or routers.

Computer worms are able to find their way from device to device by exploiting technical vulnerabilities in networks and operating systems.

Infographic showing how computer worms spread through networks

Different Types of Computer Worms

Computer worms can affect every kind of operating system. Whether you have Windows, Linux, iOS, or an Android device, there will always be a custom-made piece of malicious code that’s able to burrow its way into your computer’s operating system or mobile device.

While they are tailored for each operating system, there are different types of worms that behave differently from one another in the way they do damage. Here’s a rundown of the different types of worms.

Types of computer worms that can affect your device

Payload Worms

You can imagine a payload worm like a stealth fighter jet dropping a bomb — only this bomb is loaded with havoc-wreaking malware. This type of worm is a hybrid that both actively tries to search out new devices and install malware once it has breached the system. So essentially, the malware piggybacks on the worm and uses it to inject its harmful software. Hackers can use this type of hybrid worm to read or delete files or to install adware, spyware, or viruses.


Similar to payload worms, cryptoworms are a particularly dangerous threat, as they deliver ransomware. Ransomware attacks have become the largest cybersecurity threat in recent years. They often occur after a phishing attempt or social engineering attack, or after an attacker buys corporate access on the dark web. Once the breach is complete, cryptoworms are able to work their way through and lock up entire networks, encrypt files, and prevent huge businesses from operating. In order to get files back and resume operations, companies and organizations must pay a ransom to hackers.

Bot worms

Bot worms effectively turn infected devices into “zombies” or “bots.” These infected devices form a network called a botnet, which a hacker or “botmaster” controls. Typically, botmasters use this botnet to carry out various cyberattacks. For example, botmasters might use this zombie network to overload a website with a large number of devices in a DDoS attack, highjack computers for illegal cryptocurrency mining schemes, or blast out spam or phishing email campaigns.

Email worms

Email worms have become quite common and are spread through spam emails. Once your computer is infected, the worm will dig through all of the addresses on your contact list and send out malicious emails to everyone on them. Once someone else’s computer is infected, the cycle continues. Some worms can even reply to emails in your inbox or sift through files to pull out email addresses, so even people who aren’t in your address book could be infected.

Instant messaging worms

Though computer worms used to be more commonly spread through emails, nowadays social media is ripe for infection. At some point, you’ve probably seen strange messages directing you to click a link from a Facebook or Twitter contact you haven’t spoken to in years. This is a common way computer worms burrow into systems.

Internet worms

Internet worms take advantage of websites that are poorly or improperly secured. Once an internet worm is able to infiltrate the site, any visitor to that site can be infected. Like other worms, once it’s on your computer, it can latch onto local networks and private connections.

File sharing worms

These worms take advantage of peer-to-peer file sharing and torrent sites since the user can never be totally sure what they’re downloading. While they think they might be downloading a movie, TV series, or video game, they could be downloading a worm ready to infiltrate their entire network of systems. If you want to learn more about protecting yourself while file sharing, make sure to check out our full article on safe torrenting here.

Ethical worms

There is also a type of worm called an “ethical” worm. These worms don’t have malicious software attached to them, but carry updates or patches for known security leaks instead. They “infect” older systems that have security issues and dump a payload of fixes. Ethical worms have fallen out of favor, however, as some cybersecurity experts object to their invasive approach.

How Do you Prevent Computer Worm Infection?

Though worms are sneaky and can install themselves onto a system with ease, there are three easy steps you can take to prevent computer worm infection.

1. Get premium antivirus software

The first line of defense against any and all malware is a strong antivirus program. Good protective services will stop you before you enter malicious sites or click on phishing emails. Antivirus software is also able to block bad connections that might allow internet or file sharing worms to latch onto your device.

Solid antivirus will also allow you to set up a firewall, which can block worms and malicious programs before they access your device.

Finally, if a worm does somehow get onto your system, you’ll need the program to root it out, quarantine it, and destroy it. Want a recommendation? If you’re looking for top-notch worm and malware protection, we recommend Malwarebytes. You can read more about Malwarebytes in our extensive antivirus review, or head directly to the Malwarebytes website by clicking the button below.

Check out Malwarebytes for top protection

2. Update your system and software

As we mentioned before, computer worms exploit vulnerabilities in operating systems and software on your device and network. If you don’t update regularly, you won’t have all the latest security patches and fixes for Windows, iOS, or any other operating system you’re using. So, next time your device tells you it’s time for an update, don’t postpone it and plan it in right away.

When you’re using antivirus software, also make sure to keep that updated regularly and to run daily or weekly scans on your devices.

3. Educate yourself and be vigilant

The fact that you’re reading up on protecting yourself already gives you a layer of protection. The more you know, the more vigilant you can be. It’s crucial to be aware of common computer worms and how they attack. Pay attention to strange emails and be cautious when opening files attached to emails. Unless you’re expecting a download or attachment from someone you totally trust, you should never click on any links, websites, or attachments.

Social media has also become a prime spreading ground for computer worms. Oftentimes you’ll see a link from someone you don’t regularly speak with, or suspect that someone’s account has been compromised by their posts or stories. The same advice applies here: if you don’t expect to receive a message, download, or link from one of your connections, don’t click on it. All it takes is one click on a fake video clip and a worm could access your device and network.

What’s the Difference Between a Computer Virus and Computer Worm?

People are often confused about whether a computer virus and a computer worm are the same thing or not. They aren’t. Worms and viruses are different in one essential way:

  • A computer virus must be activated by a device user — usually through a download or clicking a malicious link that leads to an unwanted download. Once activated, the virus runs its attack on a specific device. In order for the virus to spread to another device, another host must mistakenly download it or click a malicious link.
  • Worms can be spread this way too, but they’re much more dangerous because they don’t have to be. Worms can infest devices by simply replicating themselves through networks and internet connections. Even if you don’t click any bad links or virus-riddled attachments, worms can still find their way to your system.

Computer viruses and worms can perform an attack together, too. As discussed before, worms can carry viruses in their payload. Probably the worst-case scenario would be for a payload worm carrying devastating viruses or ransomware to infect your system. Your device and network could face serious consequences when the worm downloads the virus onto your system.

How to Detect a Computer Worm

It can be quite difficult to figure out whether your device has been infected with a worm or not. Some symptoms of a computer worm infection also apply to other types of malware, or they might even mean that your computer is simply getting old. However, if your computer shows more than one of these symptoms, there’s a good chance it’s infected:

  • Your computer freezes or crashes repeatedly.
  • Your computer makes strange noises or shows strange messages or pictures.
  • You get a message from your firewall.
  • Files have been altered, but not by you.
  • You get an error message from your operating system.
  • You are missing important files.
  • Strange files or shortcuts appear on your desktop.
  • Your computer is slow.
  • Your browser is slow or doesn’t work.
  • Messages are sent to people from your contact list without you knowing, either through email or social media.

How to Get Rid of a Computer Worm

Removing computer worms can be a tricky task, but it’s certainly not impossible — especially with high-quality antivirus software. Premium programs are constantly updated on the most recent worm threats and can not only pinpoint the worm, but also delete any viruses or other malware that has come along with it.

Here are a few pointers to wring out any worms that might have affected your system:

  1. Get off your local network: Since worms work their way through networks and the internet, make sure to disconnect from any network that may be compromised. If you believe your office network is infected, contact your IT department. If it’s another LAN network, contact your Internet Service Provider (ISP).
  2. Run a deep system scan: Use your antivirus to run the most detailed scan, instead of just a “quick scan.” Make sure you’ve updated to the latest version of the antivirus software before you run it.
  3. Approve virus and worm deletion: Programs will often need permission or approval to quarantine and delete malware. If you’ve got a premium program like Malwarebytes, Bitdefender, or Kaspersky, make sure to let it do its job and give approval.
  4. Update to real-time protection: Good antivirus software has options for real-time protection so it can catch threats before they become a problem. This will also allow the program to run daily or weekly scans in the background, so you won’t have to worry about future infections.
  5. Set up a firewall: Premium antivirus software programs also have firewalls that create a strong barrier between your device and malicious entities. Make sure to turn it on if it isn’t already.
  6. Check external storage: Though infection due to external storage devices (like USB sticks) isn’t as common as other methods we’ve discussed, the possibility is still there. Run virus scans on USBs and other external devices to make sure there aren’t any worms hiding there.

Historical Computer Worm Attacks

Though fiction authors already wrote about computer worms and viruses in the 1970s and early 1980s, the actual history of worm attacks didn’t start until 1988. Here’s a quick rundown of some of the largest worm attacks in recent history.

The Morris worm, 1988

The first known worm attack was from a computer science student at Cornell University. Robert Morris created the self-replicating worm program and released it onto the internet from another university (Massachusetts Institute of Technology) in hopes of no one would find out he was the culprit. The Morris worm filled up the memory banks of devices — and managed to affect nearly one-tenth of the internet’s users at the time. As it was the internet’s early days, those numbers aren’t as big as they are now: it affected around 60,000 systems connected to the ARPANET network.

ILOVEYOU worm, 2000

The most devastating email worm in modern history, ILOVEYOU, began replicating itself after users initially opened a malicious attachment. ILOVEYOU would then send itself through IM chats and Microsoft Outlook email address contacts. This email worm reportedly affected nearly 45 million users by the time it was contained. It even forced the Ford Motor Company to shut down its email systems.

WannaCry worm, 2017

WannaCry is a cryptoworm carrying the notorious WannaCry ransomware code. It affected large companies using Windows operating systems by exploiting security vulnerabilities. Once inside the system, the ransomware would encrypt files to make them impossible to access. Once files were encrypted, hackers sent a message demanding payment for a decryption key. WannaCry hackers targeted banks, medical centers, and FedEx.

Final Thoughts

Computer worms are harmful types of malware that can cause a lot of trouble. These worms automatically find their way around a network to spread malware over all the connected devices.

There are many types of worms, which means that, if you get infected, you need to find out how to deal with your specific worm accordingly. You can protect yourself against worms by keeping your operating system and software up-to-date and by keeping an eye out for strange messages or links.

And most importantly, always protect yourself with top-tier antivirus and security software.

What is a Computer Worm? How Do You Prevent Them? | FAQs

Got questions on computer worms and how to root them out? Click on one of our frequently asked questions below.

Computer worms are malware programs that get installed on user devices through phishing emails, malicious attachments, or social engineering attacks. Once the initial attack is complete, worms are able to self-replicate and infect connected networks and devices. Read our full article to find out more about computer worms, how to prevent infection, and how to get rid of them.

Unlike viruses, computer worms are malware programs that can spread across devices and networks without any human activation — like clicking malicious links or downloading an attachment. Some examples are:

  • The Morris worm in 1988 (which infiltrated nearly one-tenth of the internet’s users at the time)
  • The ILOVEYOU worm in 2000
  • The ransomware-injecting WannaCry cryptoworm in 2017

While some computer worms are more of a nuisance, some are extremely dangerous and can have devastating consequences for businesses and individuals. Some worms can carry ransomware and other types of malware and install it automatically. You can read about different kinds of worms and how dangerous they are in our article on computer worms.

Computer worms are initially spread through phishing emails, malicious downloads, or social engineering attacks. After the first breach, they self-replicate and infect networks and systems connected to the first victim. From there, they spread through security vulnerabilities in operating systems and software.

Computer viruses must be activated by a human user. This is usually due to clicking a malicious link that triggers a download of the worm. Social engineering tactics and phishing emails are often used in these attacks. You can read more about computer viruses here.

While the first download of a computer worm happens the same way, worms can self-replicate and spread through vulnerabilities in networks, operating systems, and software on their own after that, with no human activation.

To remove a worm, you need to:

  1. Disconnect from networks and websites that could possibly be infected.
  2. Run a deep, full system scan with your antivirus software.
  3. Once the antivirus software has rooted out the worm, you must quarantine it and delete it.
  4. You’ll probably need to restart your device as well.

Make sure to use good, premium antivirus software that stays up-to-date on the latest computer worm threats.

Tech journalist
Taylor is a tech writer and online journalist with a special interest in cybersecurity and online privacy. He’s covered everything from sports and crime, to explosive startups, AI, cybercrime, FinTech, and cryptocurrency. For VPNOverview.com he follows news and developments in online privacy, cybersecurity, and internet freedom.