The main reason people write malware is to hurt others and make money, usually by stealing or deleting important information. The Cryptolocker computer virus, for example, makes it so a person cannot use their own computer until they pay the malware writers for a software key to unlock it. Another virus, CIH, tries to make it so the victim can never use their files or turn on their computer again. Malicious keystroke logging software remembers everything a user types in and gives it to the malware author to read.