What does anti virus software protect against?

Answer 1

Anti-virus software is intended to detect and protect computer systems against the types of malware known as viruses and worms. The better ones will attempt to repair systems that are infected and delete the malware when possible and at least quarantine it where it cannot execute if it is impossible to clean it up. A worm is a piece of malware that propagates itsself across the network without the user doing anything. A virus generally does something bad to the computer when the user executes it. The virus may be a stand-alone piece of software or attached to another program (also known as a "trojan horse"). The anti-spyware does this either by recognizing a "signature" for the virus - a piece of code that is unique to the virus, or by heuristic methods - looking at the behavior of the software to detect it doing things that are typical of viruses.

Anti-virus software does NOT protect against spam, spyware, or adware although many antivirus programs have integrated anti-spyware and anti-adware functionality into their products.