Some intruders cause trouble by reformatting your hard drive, changing your data, or by watching all your actions on the computer.

Unauthorized people who try to break into computers, either in a local network or using the Internet are called intruders. They may not care about your identity. Often they want to gain control of your computer so they can use it to launch attacks on other computer systems. Having control of your computer gives them the ability to hide their true location as they launch attacks, often against high-profile computer systems such as government or financial systems. Even if you have a computer connected to the Internet only to play the latest games or to send email to friends and family, your computer may be a target.