Account pre-hijacking is when someone takes over your online account without you knowing. This can happen in lots of different ways. For example, someone could guess your password, or use a piece of software to try to guess it. They could also find out information about you (like your name, birthday, address, etc.) and use that to get access to your account. The most important thing you can do to protect yourself from this is to have a secure, difficult-to-guess password.