Unfortunately it has come to light that the program ComboFix had a file in it that is infected with the Sality virus. The minute we heard about this, we pulled the executable so that it is no longer available from BleepingComputer.com. Unfortunately we have no control over other sites that may have mirrored ComboFix without permission, so please do not attempt to download it elsewhere.
The developer, sUBs, is currently looking into what happened and when I have a full update, I will be sure to let you know. From the limited information that I have, it appears that the affected version has been available since approximately 2am EST on January 29th, but it may have been earlier. If this timeframe changes, I will update this topic to let you know. If you have used a new copy of ComboFix in the last day or so, then you should examine your system for possible infection. If you have used a copy of ComboFix prior to this version, then you should be ok.