Malware, short for malicious software, comes in various types designed to harm or exploit devices. Common types include viruses, which attach themselves to clean files and spread to other files, and worms, which replicate themselves to spread across networks. Trojan horses disguise themselves as legitimate software to trick users into installing them, while ransomware locks users out of their files until a ransom is paid. Another type is spyware, which secretly monitors user activity and collects personal information. Adware displays unwanted advertisements, often slowing down devices. Lastly, rootkits enable unauthorized users to gain control over a system without detection, posing significant security risks.