What does this alert mean?

Win 7 64 bit

services exe is about to modify the windows service registry root HKLM/SYSTEM/ControlSet0012\services\BITs. Says it is unusual and usually dealt with by defense. Should i allow it?

You can allow it and make CIS remember the answer.

BITS is part of Windows updater; its full name is Background Intelligent Transfer Service and deals with downloading the upates in the background.