I have had major problems with this today. Something caused ALL the Norton virus definitions to be deleted (or I assume it could have been all of them, as the required download was huge). Of course, Norton displayed 'At Risk', and the computer complained of no anti-virus software. The computer was also periodically doing blue screen of death (switched off before I had a hope of getting what the blue screen said), so it was a mission between normal & safe mode to get the definitions file back. But we got there.
So we scanned, in safe mode, and nothing was found. But the blue screen problem persisted in normal. So in goes the faithful Linux boot memory stick, to run some tests without blue screens! It (clamscan) has found an infected file called trojan.autoit.gen in
ProgramData/Norton/***random numbers/digits***/Definitions/VirusDefs/20101004.003/virusScan9.dat: trojan.autoit.gen
We are using Norton Internet Security 2010 with Windows7. Any help gratefully appreciated as this PC is used for a home business. Thanks!