Malware is software designed to damage computers, steal information, or cause problems for users. The word combines “malicious” (meaning harmful or evil) and “software” (programs that run on computers).

When malware infects a computer, it might delete important files, slow everything down, steal passwords, or spy on what you're doing. Computer viruses are one type of malware: they spread from computer to computer like a real virus spreads between people. Other types include spyware that secretly watches what you do, and ransomware that locks your files and demands payment to unlock them.

Malware usually sneaks onto computers through tricks. Someone might click on a suspicious email attachment, download a game from an untrustworthy website, or plug in an infected USB drive. Once inside, it can cause serious harm: deleting homework, stealing credit card numbers, or even making the computer unusable.

Computer security experts work constantly to detect and stop malware. They create antivirus software that scans for known malware and removes it. Meanwhile, criminals keep creating new malware, making computer security an ongoing challenge. The best defense includes being careful about what you download, keeping security software updated, and thinking twice before clicking on links from strangers.