A computer virus is executable code that has the ability to copy itself. It can spread quickly and is often difficult to identify and eradicate. It can attach itself to a disk file or an e-mail and is spread as these items are sent from computer to computer. In addition to replication, some contain damage routines, which deliver the virus payload. A wide variety of viruses exist, some of which can even steal information from your computer secretly.
Viruses range from the most dangerous to the benign.
Start with the basics. Several commercial virus protection packages are available. Most have teams of programmers that update their associated websites on a daily basis. This will stop most viruses. Also, be wary of any unexpected emails.