A computer virus is a program designed to replicate and spread on its own, usually without a person’s knowledge. Some symptoms of boot sector virus activity include: One cannot launch Windows, One’s computer cannot perform a disk-based setup, One gets diskette errors, One gets hard drive errors, and One gets non-system disk errors. Viruses, whether they are boot viruses, file viruses, or macro viruses, can employ none, one, or several of the following techniques to spread or conceal themselves. Multi-partite viruses often infect multiple targets instead of just one type of file or disk. A polymorphic virus change segments of its own code so that it looks like a different virus from one infection to another. Retro viruses are designed to actively attack anti-virus software. Triggered event viruses activate based on some event. Memory-resident viruses are copied to the computer’s memory when its host program is executed. A non-memory-resident viruses becomes memory resident when the host program is executed.