Computer worms are one of the most common types of malware. Not to be confused with viruses, they are characterized by their ability to run without a host program. Most viruses need a host program to run. Worms, on the other hand, can run by exploiting vulnerabilities in operating systems (OSs) and other software. By understanding how they work, you can better protect your computer and network from worms.


Like most other types of malware, worms must infect computers before they can execute their malicious code. Infection can occur in different ways. Phishing, for instance, may result in a worm infecting your computer. You may follow a link in an email, only for it to deploy a worm.

Some worms can spread throughout networks. If there’s another computer on your network that’s already been infected with a worm, the worm may spread to your computer. Even external hardware devices, such as Universal Serial Bus (USB) flash drives, can carry worms. Inserting an infected USB flash drive into your computer’s USB port may spread the infection to your computer.

Common symptoms that your computer has been infected by a worm include the following:

  • Windows Blue Screen of Death (BSOD)
  • Slow speeds
  • Random reboots
  • Programs crashing
  • Unknown processes running in Task Manager
  • Firewall notifications
  • OS settings automatically changed
  • Antivirus software warnings


Worms have a payload. The payload is the malicious code that worms use to both spread and run their malicious code. Some worm payloads are designed to install a backdoor so that the hacker behind the worm can access an otherwise secure network or database. Other worm payloads are designed to delete data. Regardless, worms have a payload. They’ll use this payload to both spread and run their malicious code.

No Human Intervention Required

One of the defining characteristics of worms is that they don’t require human intervention. This makes them a particularly troubling type of malware. If a worm infects your computer, it may spread while simultaneously executing its payload — regardless of whether you open or run any other programs.

Viruses, on the other hand, do require human intervention. You’ll typically need to run the host program in order for the virus to execute its malicious code. Unless you open and run the host program, the virus won’t harm your computer. Worms are considered more harmful than viruses because they don’t rely on a host program. They can spread and execute their malicious code on their own.