What Is a Computer Worm?

Just like real-life parasites, computer worms duplicate and spread from one computer to another. But how do they do that? How much harm can they cause? And are they any different from computer viruses? Read this blog post to find out.

What is a computer worm?

A computer worm is a type of malware that multiplies and spreads from one device to another. It doesn’t require any human interaction and doesn’t need to be attached to any software.

Computer worm vs. virus: What’s the difference?

Worms and viruses are two of the most common types of malware that can infect computers and other devices. The main difference between the two is that worms propagate and spread independently. They are standalone files or software.

A computer virus, on the other hand, is malicious software that needs a host to spread. They usually need to use brute-force to get into your device — for example, they might trick you into downloading them by clicking on a malicious link or fake software. They cannot infect devices on their own accord.

How do computer worms spread?

Worms are designed to spread like real-life parasites. They exploit vulnerabilities that already exist at the computer's operating system level. They then travel through a computer network, duplicating from one computer (or host) to another. Computer worms rarely infect files — what they do is eat up your hard drive space or internet bandwidth.

However, some worms might carry a malicious payload that can make your computer vulnerable to malware, ransomware and DDoS attacks. As worms usually target operating system vulnerabilities, security patches are released for them regularly, so developing payload-less worms isn’t worth the hassle anymore. This is why hackers use worms with malicious payload to target big organizations and governments, and perform larger-scale attacks.

Computer worm examples

As worms usually don’t do much harm other than slow down your device, such attacks are mostly used by novice hackers who want to practice their skills and annoy users. However, the very first worm, called the Morris worm, received significant media attention and resulted in a first-ever conviction for computer fraud. It wreaked havoc on the internet for several days and infected around 10% of computers worldwide. The hacker who developed this worm said it was never intended to cause so much harm, but was simply meant to highlight security vulnerabilities

Other known worms that wreaked havoc globally were:

  • SQL Slammer, which infected most SQL servers worldwide;

  • Blaster performed a DDoS attack on Microsoft servers and affected millions of computers;

  • Conficker created a botnet made out of millions of infected computers;

  • Stuxnet, which was a state-sponsored attack directed at Iran’s nuclear program, set Iran’s advancements way back in time.

The problem with computer worms is that their creators never expect them to spread so widely and cause so much damage. Some of them were never intended to reach the average user, yet they did. Once worms start spreading, they become almost uncontrollable. They are also somewhat difficult to detect and get rid of.

How to identify a worm on your device

  1. Check your hard drive space. Has it suddenly dropped? As computer worms replicate themselves, they will start eating up the space on your device without your knowledge.

  2. Monitor the speed and overall performance of your computer, as computer worms could be eating up its processing power. If your device has suddenly started responding to your commands in a much slower fashion, it may be a sign of a worm.

  3. Keep an eye on your files, as worms tend to delete or replicate them.

  4. Run an antivirus scan. Since worms don’t need a host and are not software, they are especially challenging to detect. This means that not all antivirus programs will pick up on them, but it’s always worth double-checking.

  5. If the worm carries malicious payload and opens the door to other attacks, such as ransomware, DDoS, and cryptojacking, it might be next to impossible to remove it and you may need a professional’s help.

How to prevent worm infections

  1. Keep your operating system and apps up to date. Install security patches as and when they are released. Patches exist for a reason, as they can help you prevent or put a stop to worms or other computer viruses.

  2. Learn to recognize phishing. One of the most common ways to spread malware or worms with payload is through phishing emails or social media messages. If you receive an email or an instant message from a friend, asking you to click on a link or an email attachment, don’t do it. It’s probably a trap — especially if they are offering you a good deal.

  3. Use security tools that will help you identify security vulnerabilities. Invest in a good antivirus and anti-malware software.

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