New legislation effective today in the UK (or should I say NOT very effective??

) renders UK spammers liable to a fine of £5000 if caught. Given that this will not really help much, some Q's for the Gurus:-
1) In the past, some of my private forum members' machines have unwittingly been set up by hackers to send out 'under-cover' spam. Is there any way a user can tell if this is happening eg internet/email logs anywhere on the machine or some registry entries?
2) Is there any guaranteed way to check that one's Virus Checker is functioning and not been hacked, other than visiting 'Housecall' at intervals or sending oneself a test virus?