I recently tried the (free for home use) Avast Antivirus program and am very pleased with the way it updates automatically etc. but, I couldn’t find a virus vault or any mention of it killing a virus once it had detected it. Does it remove the virus or just tell you it found one?
Gus 
Of course, avast can help you getting rid of the virus. Only a limited number of viruses can be “healed” as such (most notable the macro viruses). For the viruses/worms that avast cannot heal directly, it gives you the possibility to e.g. move or delete the infected file (s), or move them to the Virus Chest (the Vault, as you call it).
Vlk
Thanks for the clarification. Approximately how many viruses does Avast recognize according to it’s virus definitions which I gather are constantly being updated???
Once again thank you for the very quick response and for producing such a great free for personal use product. I am living on a fixed income since retirement and cannot afford to purchase many programs for my system but would like to ensure that at least my system remains virus free.
Gus:
Approximately how many viruses does Avast recognize according to it's virus definitions which I gather are constantly being updated????
All of 'em. 
And the updates are necessary because new viruses appear (almost) every day.
Anyway it’s pointless to say “how many” as there are no ‘naming standards’ – for a more detailed discussion, please see e.g. this thread: http://www.avast.com/forum/index.php?board=2;action=display;threadid=200;start=0
Hope this helps,
Vlk