AVG Signal Blog Security Viruses Worm vs. Virus: What's the Difference?

Written by Nica Latto
Published on December 18, 2020

What is the main difference between a worm and a virus?

The main difference between a computer worm and a computer virus is that worms can spread independently, without being attached to a host file or program. Some people describe computer worms as a subset of computer viruses, but it’s more common to consider worms and viruses as two subcategories of malicious software (malware).

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    But let’s take a step back: Malware refers to all malicious software and code, which is created to damage files and devices, mine and exploit personal data, and generally wreak havoc — usually to make hackers money. And while some people use the term “virus” to refer to all malicious code, a virus is just one of the many types of malware.

    The main difference between worms vs. viruses is how they spread and how they behave.

    Computer worms and computer viruses as two subcategories of malware.Computer viruses and worms are both types of malware.

    How a computer virus spreads

    A virus infects your device by inserting its code (or payload) into a program or file and borrowing your system’s resources to copy itself and spread. That’s why viruses are sometimes referred to as “file infectors.”

    A computer virus lives within a host, such as a document or executable file, and requires human interaction to spread. That means a virus lies dormant until you inadvertently trigger it by executing the file.

    Once active, a self-replicating virus starts to copy itself and spread. Viruses can cause many forms of damage, such as corrupting files or apps, harming your computer performance, and infecting more and more devices (and people). 

    An example of a virus infection

    Here’s a typical example of how you can get infected by a computer virus: You receive an email (that you’re not expecting) with an intriguing (clickbait) title like “Made some changes — please check.” Attached to the email is a file with a name like “Updates” — it may be a DOC or EXE file.

    A computer virus lives within a host, such as a document or executable file, and requires human interaction to spread.

    If it’s a DOC file, once you download it, you’ll be prompted to enable macros (programmed rules that help simplify repetitive tasks). This action triggers the virus. 

    If the file is an EXE, downloading it and running it triggers the virus. The virus will then commandeer your computer’s resources to copy itself and spread, damaging your devices and files or stealing your personal data.

    How a computer worm spreads

    A worm is different from a virus, because it doesn’t require a host or human interaction to spread and wreak havoc. It’s also self-replicating malware, but it’s the stand-alone variety. Worms often spread through a software vulnerability.

    A security flaw, or vulnerability, is created accidentally by developers while they’re writing a program or developing an operating system. Hackers later discover the vulnerability, and write code to exploit it. They use the exploit to push malware in through the uncovered “hole” and into your system. The scary part is that you may have no idea you’ve been infected. 

    A worm is different from a virus, because it doesn’t require a host or human interaction to spread and wreak havoc.

    Some security flaws are so dangerous that they become notorious — like EternalBlue, which caused the colossal WannaCry attack, or BlueKeep, which may still affect one million Windows PCs.

    Once a worm is in your system, it can scan the network to detect any other devices that contain the same vulnerability. The worm then jumps to all of those devices, infecting them and repeating the process all over again. A worm can also spread through an infected file or program.

    An example of a worm infection

    Here’s a typical example of getting a worm infection: You get a notification that Windows has a critical security update. But you’re busy doing something else, so you ignore it, and then forget to install it later. That update was intended to fix a security vulnerability, but since you didn’t apply the update, the hole (vulnerability) remains in your system. 

    Sooner or later, an enterprising hacker finds this hole and exploits it. Then, while you’re busy working or gaming, a worm burrows into your computer and begins replicating itself, compromising your data and causing all kinds of other damage. 

    Before you have a chance to realize what’s happening, the worm scans your network. It finds that you haven’t applied the update on your other computer either, and neither has your spouse. The worm quickly spreads to all those devices, too. 

    Still unaware of any problem, you decide to head out for a cup of coffee. You sit down with your laptop at your local café and connect to their Wi-Fi. The worm scans the coffee shop’s network, finding and infecting a dozen more devices (and people) that have the same vulnerability. Those people eventually go home, and their devices then infect their family members’ devices too, and so on.

    Summarizing the differences between viruses and worms

    Virus Worm
    • Requires a host

    • Triggered by human interaction

    • Often arrives through an infected file or program (file-infector)

    • Spreads independently 

    • Doesn’t require human interaction

    • Often arrives through a software vulnerability

    There are similarities, too

    Despite the distinctions outlined above, worms and viruses do behave similarly in other respects. The main similarity is that both viruses and worms self-replicate and spread rapidly. In fact, both can spread exponentially, giving them extreme potential for damage. When it comes to viruses vs. worms, it’s safe to say you want to stay far away from both.

    Computer viruses and computer worms self-replicate and can spread exponentially.Both viruses and worms can spread exponentially.

    Which is more dangerous, a computer virus or worm?

    Though there can be a scale of danger among viruses and worms, worms are generally considered more dangerous. Worms are sneakier, because they can infect you without you even realizing it. And new strains of viruses (or file-infectors) are hard to find these days, while worms are much more common.

    Both worms and viruses have huge potential to cause security and privacy problems. A minor malware infection can damage files, programs, or devices. But more damaging infections can steal your sensitive personal data, which could lead to identity fraud and monetary theft. 

    Small companies, large corporations, health care systems, and even countries can be hit hard by malware. Viruses and worms can cause large scale data leaks, data loss or theft, expensive repair costs, reputational damage, and even cyberwarfare.

    Blended threats

    The most dangerous cyberthreats are those that combine aspects of different types of malware. That could be adware that mimics spyware to surveil you — or track your behavior online — while also bombarding you with ads.

    On a larger scale, a well-known example of a blended threat is WannaCry. A wormable form of ransomware, WannaCry spread to 10,000 PCs per hour in 150 countries, encrypting devices and demanding a ransom to decrypt them. This ransomware worm spread exponentially, causing $4 billion in damage to hospitals, universities, governments, and other entities.

    Whether or not a virus, worm, or blended threat has infected your machine, you need a powerful antivirus to keep you safe whenever you’re connected to the internet. AVG AntiVirus FREE provides continuous threat protection to make sure your personal information is secure at all times. Plus, it’s completely free, so there’s no reason not to use it to keep your computer, your data, and your family safe.

    Virus vs. worm: which one do I have?

    All types of malware have some similar traits and characteristics. That can make it extremely difficult to determine which form of malicious software you have, because they can cause very similar symptoms. In general, look out for these tell-tale signs of a malware infection:

    • Unexplained slow performance

    • Changed settings or new apps that you didn’t configure yourself

    • Lots of crashes or freezes

    • Missing or corrupted files

    • A hyperactive processor

    • Sudden loss of storage space

    • Tons of pop-ups

    If you notice any of these symptoms, it’s time to find out what’s plaguing your machine.

    What to do if you have a virus or worm?

    If your device is suffering from any of the malware symptoms above, you should immediately perform a malware scan. Unless you’re a malware expert, it can be extremely difficult to find and diagnose the infection yourself.

    That’s why we recommend using a free virus removal tool that will find whatever’s lurking on your machine and delete it immediately. No matter which device you use, we can help you remove viruses, worms, and all other types of malware safely with AVG AntiVirus FREE. See our guides for more details on how to do this on particular devices:

    How to protect yourself

    An ounce of prevention is worth a pound of cure, as the old adage goes, and that applies tenfold when it comes to viruses and worms. Learn how to protect yourself now and you’ll never have to worry about damaged files, stolen personal data, or spreading the infection to your friends and family in the future.

    icon_01Avoid opening suspicious emails and links

    When it comes to the internet, a healthy dose of skepticism is often warranted. Don’t open emails from unknown sources. Even if it’s from a trusted contact, but it doesn’t sound like them, proceed cautiously. Their device may be infected with malware that’s now spamming their contacts. Be especially careful with links and attachments. That includes links you receive on messaging apps and social media. 

    icon_02Download apps and media only from trusted sources

    Apple’s App Store and the Google Play store vet developers and their apps and test them for security. While it’s not 100% foolproof, it’s much safer than downloading programs on a third-party website. 

    But if you really want to download something from an unknown website, make sure to verify that the website is safe. You should also avoid torrenting movies and music. Not only is it illegal, torrent files may be infected with malware.

    icon_03Use an ad blocker

    Malvertising refers to infected ads that can spread malware on your device if you click on them. Malvertising can also insert malware into ad networks that distribute ads across the internet. That means malicious ads can show up even on legitimate, trustworthy sites. An ad blocker will prevent ads from loading, so you never even see them. And an ad blocker will also help prevent drive-by downloads, whereby infected ads get into your system without even being clicked on.

    icon_04Use a trusted antivirus

    Viruses, worms, Trojans, ransomware — you can prevent them all with a robust cybersecurity tool like AVG AntiVirus FREE. AVG provides 24/7 protection to detect and block all types of malware before it can get anywhere near your system. And extra, built-in defenses against infected email attachments, malicious downloads, and unsafe links means you always stay safe against the most common virus and worm vectors.

    icon_05Don’t connect to unsecured networks without a VPN 

    Unsecured Wi-Fi networks are common in public places like coffee shops, airports, and malls. And while they’re usually free, you might pay the price later when a hacker intercepts your personal data. These networks are just too easy for hackers to crack. To connect to them safely, use a VPN, or virtual private network. 

    A VPN, like AVG Secure VPN, encrypts all your traffic, creating a secure private tunnel for your device to reach the internet. With a VPN, no one can spy on you, so you can surf, bank, and shop securely, even in public.

    icon_06Keep your operating system up-to-date

    No matter how annoying those update notifications are when they interrupt you, they’re absolutely crucial for maintaining your security. Recall that hackers can exploit security holes to push worms and other malware into your system. You can avoid that easily by applying security updates to your operating system and programs in time, every time. 

    So, the next time you get that update notification, don’t push “remind me later” — do it immediately. It’ll be worth it.

    Block worms and viruses with AVG AntiVirus FREE

    Employing smart digital habits like those described above will go a long way toward keeping you safe online. But no matter how careful you are, there’s no guarantee that a sneaky hacker won’t be able to slip some malware your way. 

    Get complete protection against viruses, worms, ransomware, and other malicious code with a comprehensive antivirus solution. AVG AntiVirus FREE uses advanced cloud-based AI to provide six layers of protection. Download it today to secure your computer and get peace of mind.

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    Nica Latto