My friend and I both use AVAST (Home edition 4.1). But last week his hard drive crashed.
He downloaded and used AVG Anti Virus software and ran it on another hard drive and scanned the “crashed” hard drive. It found two trojan viruses called ‘backdoor.litmus.ce’ and ‘irc/backdoor.sdbot.20.bn’.
Shouldn’t Avast prevented those trojans from infecting his system? He updates the virus definition table OFTEN.
Avast automaticly checks for updates as soon as a connection to the net is established. After that it checks every 4 hours.
I think your friend had either Avst not running or changed a setting so it didn't scan like it was supposed to.
Paul, besides the antivirus, there are a lot of other important security actions to be taken: update your antivirus, update your operational system and Internet programs, use spam/spyware killers, firewall, etc. etc.
Maybe the fault is not avast but some other of this rules…