What do Anti virus programs actually do?

[SkipAAN]

Can someone please explain to me what Avast actually does.  And what is this virus chest thing?  Because it seems to me that Avast (like all other anti-virus software I have used) can only report infections, but can't really do anything about it, except delete the file.

[Vladimyr]

That's the essence of it. Detect potentially malicious files as they are accessed or written, remove, delete or quarantine them (in avast's case, the "chest thing") just in case they aren't malicious after all. It's also good if the program updates itself automatically and makes little impact on your PCs speed.

[George Yves]

To cure a sick man the doctor should know the normal health conditions of his patient; to cure an infected file the antivirus should know the normal "health conditions" of the file. The doctor uses his medical university knowledge and experience; Avast uses VRDB. So, updating VRDB regularly you secure your PC's files from being incurably infected and later you can restore your system to its normal "health conditions".

If the doctor can't cure a patient immediately, he doesn't kill him: he puts such a patient into quarantine (he needs time to consult other specialists). If Avast can't cure a file immediately, he doesn't delete it: he - upon your decision - moves it into quarantine (Chest). You can later consult with other on-line antivirus services if you want to cure the file.

And more: to prevent an infection is cheaper than to cure it.