Personally, I think the file was erroneously identified as a MacKeeper file, possibly because its name was similar to one….
I wonder if that's also the case with my mysterious document. I subsequently closed everything, including DetectX. I then re-opened it and ran another search. This time DectectX didn't find anything and gave me a 'thumbs up'.
Don't know if it will work, but have you tried "rm"ing it in Terminal?
While it now seems the file may not be MacKeeper, there are about 20 copies of the file instead of one. For the sake of keeping things tidy I wouldn't mind removing all the redundant copies. Do you know what the Terminal command would be? Or is it even possible to remove all but one?