I'm having the same problem on multiple machines with xp, windows 7 has not yet happened.
I use Office 2010, I began to look crazy DDS, GMER, Combofix, MBAM and others, and always after login explorer froze and did not get any incident program, open the task manager, kill explorer, when ordered to start the explorer . exe manager crashed, I'm solving this problem going into safe mode, clearing the restore points with CCleaner, turn off system restore points, uninstall avast, start normally and it usually occurs, the explorer opens, the services begin properly, reinstall avast, active again and restart the system restore points and voala okay ...
Users here is not like the system recovery, the more we have to take into account that most do not have the knowledge to acknowledge even this bug, and end up formatting the machine thinking they are infected ...
curiosity ... after uninstalling avast, I run ComboFix and it always deletes the folder "C: \ Windows \ CSC \ D6"
every time I have this problem with avast ..
Marcelo.