Weird Problem

Having a weird problem with two users. Wondering if anyone has come across the same problem or has any idea on finding out the cause.

Our Antivirus program keeps giving me notifications that it keeps catching the klez virus. The weird thing aboutit, is that the notification says they are coming from two of our users, but they are not sending any email through Outlook, and no email is generated in the Sent Items folder.

The Exchange Logs are of no use, our firewall and IDS, not my doing, are not operational yet.

Anyone have any suggestions?