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

Worms and viruses are two of the most common types of malware and share many things in common. Indeed, worms are often described as a type of virus, in the same way, that a virus is a type of malware. However, there are some key differences between a worm and a virus, and we will explain them in this article.

The main difference between a worm and a virus

A virus is a type of malware that spreads by attaching itself to a file or program. The file or program can be transferred from computer to computer over a network such as the internet or via a USB stick, external drive, or another form of storage media. When a computer user opens the file or program, their computer is infected, and the virus then attaches itself to other files or applications on their system. 

Virus vs. worm: It’s all about self-replication

A worm virus is also self-replicating, but it doesn’t attach to a file or program. Instead, it moves through networks, from computer to computer, by exploiting vulnerabilities in the network. Worms are more nimble than viruses and can spread more quickly. Worms can seriously disrupt large networks, causing them to slow down by consuming huge amounts of bandwidth. When it comes to virus vs. worm, though, they are both pretty bad.

What is a worm virus: Here are some examples


Perhaps the most infamous worm of all, Koobface was one of the first malware programs to exploit the possibilities offered by social media. In 2008, social media was still in its infancy, and Facebook was relatively new. The Koobface worm infected user accounts and spread them by sending fake messages to users’ friends. Those messages claimed that Flash Player on the recipient’s computer was out of date and — who would doubt — contained a link to download the updater. When the user clicked the link, they too were infected. Once a computer was infected, the worm would display adware and attempt to persuade the owner to download paid-for software. It also formed botnets to attack more computers. 


In 2017, WannaCry caused hundreds of millions of dollars of damage to computer networks worldwide. It combined the techniques of a worm by exploiting a vulnerability in Microsoft’s SMB Version 1 file-sharing protocol, known as Eternal Blue. Any network that hadn’t patched SMB Version 1 was at risk, and that included systems belong to some of the largest organizations in the world. 

Storm Worm

In 2006, an email with the subject line ’230 dead as storm batters Europe’ was unleashed. Given that such a catastrophic event is almost unheard of in Europe, many people clicked the link it contained to read more. That link inevitably unleashed malware that infected the user’s computer and turned it into a bot to continue spreading the worm by itself, sending spam email messages.

An example of Mac Mail worm discovered in 2021

Early in 2021, a security researcher Mikko Kenttälä discovered a surprising Mac vulnerability within Apple’s Mail app. What makes this particular worm troublesome, is it requires zero clicks. The exploit works like this:

The attacker mails a user a ZIP-archive that Mail automatically unpacks under certain conditions. When unpacked, a virus file will do whatever it pleases on your computer.

How to avoid worms

Worms are less easy to avoid than most other types of malware. They exploit vulnerabilities in networks and servers rather than rely on social engineering techniques like persuading you to download software or click on a link. However, there are some things you can do:

  • Make sure the version of the operating system you are running is up to date
  • Don’t connect to unsecured Wi-Fi networks
  • Keep your web browser up to date
  • Scan your Mac regularly with an anti-malware tool

How to check if your Mac has been infected with a worm

The best way to check is to use an anti-malware tool. I use CleanMyMac X because it has a huge database of known malware, and it’s simple and quick to use. CleanMyMac X can scan your Mac regularly in the background, making sure it’s always safe from worms and other malware. Here’s how to use it.

  1. Install, and launch CleanMyMac X— here is a link to a free version
  2. Go to the CleanMyMac X menu and select Preferences.
  3. Select the Protection tab.
  4. Check the boxes next to "Enable Malware monitor" and "Look for threats in the background."
  5. Close Preferences.

By the way, this program is notarized by Apple, which means it’s free from malware code.

Now, CleanMyMac X will run in the background, periodically scanning your Mac for malware, even when the app itself isn’t running. You can also run a scan and remove malware manually, like this:

  1. Launch CleanMyMac X.
  2. Choose the Malware Removal module in the sidebar.
  3. Press Scan.
  4. If CleanMyMac finds anything, press Remove to get rid of it.

It’s especially effective for detecting worms and also adware scripts, those that hijack browser starting pages.

The difference between a worm and a virus is subtle. Essentially, one replicates by attaching itself to a file or program. In contrast, the other, the worm, replicates by exploiting a vulnerability in a network without needing to attach to another file. Both have the potential to cause huge problems and damage. However, using some real-time scanning tools, you can make sure your Mac is always safe from both.

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