I installed Kaspersky anti-virus for sendmail last week, and have been 
getting  on avg 4 messages a day stopped at server,  that had the klez 
virus attached.  Didn't realize it was that bad.  If you all don't have 
anti-virus software installed, I would recomend finding some.

Kaspersky is really good, but $, $14/mailbox (i think), can get from 
www.useice.com (local reseller).
RAV is also avail, but I did'n't like as well (a lot cheaper than KAV), 
also can get from www.useice.com, need to call they don't have it listed 
on site.

I also saw some opensource virus databases, but this is one area where I 
didn't mind spending the dollars.