Three common types of malware:

1. Viruses: A virus is a type of malware that can replicate itself and spread to other files or systems. It can cause damage to a computer system by corrupting files, stealing data, or disrupting normal operations.

2. Worms: Worms are self-replicating malware that can spread across networks and infect multiple systems. They can cause damage by consuming bandwidth, slowing down network performance, or deleting files.

3. Trojans: Trojans are malware that disguise themselves as legitimate software or files to trick users into downloading and installing them. Once installed, they can steal sensitive information, create backdoors for hackers, or damage files and systems.