Just a heads up, to potentially help others saving some time:
After running TDSSKiller with the "modules" option enabled on Win 8.1 x64, it finds a rootkit both in the registry as a hidden service with a random 8-digit numerical name as well as a driver in c;\windows\system32\drivers\xxxxxxxx.sys (with each x being a random number). Gmer and aswMBR find the same "rootkit", but only if run within a session that had TDSSKiller's "modules" switch active.
You can see the full description here: http://www.bleepingcomputer.com/forums/t/519538/gmer-aswmbr-tdsskiller-reporting-hidden-service-rootkit-what-now/
After finding the same "rootkit" on all of my PCs, I wiped one and reinstalled Windows from scratch, but found it "infected" straight away, which made me wonder whether this is a FP.
After reviewing the various logs I collected until then, I noticed that when running TDSSkiller WITHOUT the "modules" switch (e.g. no reboot), the TDSSKiller log would include the following line:
18:13:23.0976 0x1230 KLMD registered as C:\Windows\system32\drivers\38850691.sys
This entry is completely missing when running TDSSKiller with "modules" switched on.
My conclusion is that TDSSKiller is detecting itself as a rootkit in this case (as does GMER / aswMBR).
Can someone confirm this behavior?