Anti-virus software serves an important protection function if your computer is connected to a network of computers in any way, either for sharing files between computers or accessing Internet content. On the other hand, a stand-alone PC that is completely isolated from other computer systems or a network probably could be operated without any anti-virus software.

Anti-virus software will monitor your computer as you use it to detect any programs that match a set of "signatures" of known viruses, alerting you when it finds any and blocking them from running. Since the signatures are updated constantly for new known threats, it is important to update anti-virus software regularly, maybe even daily. Running anti-virus software without regular updates amounts to no protection at all, since the most dangerous viruses are usually the newest viruses.