For the first time in a while, a fairly large virus outbreak is in progress. Take a look at our statistics for mid-January 2007 and you can see the big spikes as trojan containing emails are spammed out en-masse. Our anti-spam service seems to have done an excellent job stopping them coming in.
This is a good time to double check you anti-virus subscriptions are up to date - whatever these files might be installing on your computers, it'll not be friendly...