A computer worm is a type of malware that self-replicates in order to spread to other computers, typically via a network. Unlike a virus, a worm is a standalone software and does not require a host program or human help to propagate.

Once a worm is on a network, it usually starts scanning for any potential vulnerabilities it can exploit to spread. This could be a security hole in a software application, an unpatched operating system, or even weak passwords that allow it to gain access.

The effects of a worm infection can vary greatly. Some worms may just use your computer to propagate and have little to no impact on performance. Others, however, can be quite harmful. They can delete files, encrypt data (like ransomware), use your computer to send spam, or create a backdoor for hackers to access your system.

One of the most famous examples of a computer worm is the “ILOVEYOU” worm from the year 2000. It was sent as an email attachment with the subject line “ILOVEYOU” and, when opened, it sent itself to everyone in the user’s address book. It caused extensive damage worldwide.

To protect against worms, it’s important to keep your system and applications up-to-date, use strong, unique passwords, and use a good security program that can detect and block such threats.