What is a virus?

A computer virus is a program that spreads by first infecting files or the system areas of a computer or network router's hard drive and then making copies of itself. Some viruses are harmless, others may damage data files, and some may destroy files. Viruses used to be spread when people shared floppy disks and other portable media, now viruses are primarily spread through email messages.Unlike worms, viruses often require some sort ofuser action (e.g., opening an email attachment or visiting a malicious web page) to spread.