OK, thanks again... I sometimes do share files/printers... so as you've pointed out that's a risk.

I do run frequent scans because I've had a nasty experience with a virus named "äve.exe" - it's appears with a screen duplicate of M'Softs Security Centre, and potentially can scan the PC (and installs keyloggers in your browser), sending info back to the virus-maker... if there's anything useful (such as passwords, etc) for the virus-maker to wreak even more havoc on the victim.

I used PCTools SpywareDoctor to disinfect, but that wasn't entirely successful, so I had to go back to scratch and re-install the whole PC (ensuring a complete format of the hard disk).

Since then I'm using Kaspersky Internet Suite, which was recommended to me (instead of ZoneAlarm, which doesn't detect "ave.exe"... well, it didn't for me). And an occasional check with Malwarebytes - AntiMalware.

Best Regards,
Frederick.