Here is some more interesting information. I'm not positive this is Sober.Z related but it's walking like and talking like a duck.
First I see the below DNS requests, shortly after I see many SMTP packets hitting Hotmail, AOL, Yahoo.com, Yahoo.co.uk, Progegy, etc.... Looks like it's... Sending SPAM?!?!
This I didn't expect at all, here is a trace from one of the known infected users: