Types of Malware

Malware is software written to cause harm to a computer system or its user. The name comes from "malicious software", and it includes viruses, spyware and Trojan horses.

How each one behaves

A virus can damage files and programs, and it can spread from an infected computer to other computers. It does this by attaching itself to a file or program, so it only runs when you open that file. If you copy an infected file onto a memory stick and open it on a friend's laptop, the virus can move across too. Once running, it might replace the words in a project with random symbols, or copy itself into other files so that they stop working.

Spyware records keystrokes and other personal information, then sends it to a hacker. Every key you press might be logged, so passwords typed into a game account could be captured. Spyware often stays hidden because you are less likely to remove something you cannot see.

A Trojan horse hides malicious code inside a program that appears useful. A free photo editor might work perfectly while secretly installing code that lets a hacker access your files. It relies on you being tricked into running it, rather than spreading by itself.

Since each type behaves differently, protection has to look for more than viruses alone.