A cookiemonster attack is when a hacker tries to get access to your computer or website by guessing your password. They try to guess as many passwords as they can until they get the right one. They might also try to trick you into giving them your password by pretending to be someone else or by pretending there is a problem with your computer. Once they have the password, they can do things like look at your personal information, send spam, or change your passwords so that you can't get into websites.