Infected with three hi.class trojans and one uu.class

I'm using a new Win 7 Laptop, New Internet Security, Firefox, Thunderbird, etc, . .  everything is updated properly and scans run daily, regular backups., etc.

 

NIS found these this morning.

 

uutecwv.class

hirwfee.class

hiydcxed.class

hieeyfac.class

 

Any info on this stuff?  How it's getting through?