A computer virus is a program that can replicate itself and infect a computer. However, there are other types of harmful computer code to avoid. One is called "rootkit." A rootkit is not a virus; it is "malware." You an unwittingly transfer a rootkit to your computer when you land on an "attack" Web site while surfing the Internet. A rootkit hides inside critical files you can't delete without making your computer become nonfunctional. The rootkit then permits third-party criminals to steal personal information on your computer without being detected. At home, use virus-protection software that will spot rootkit malware. If your computer becomes infected, you may need an expert to help remote it. At work, follow computer use rules. Never violate your employer's computer use policies.