Sorry to be that late to clarify: It does not mean you have it on your system, Spybot just scans your system for Win32.Qhost.ahnj. It works like this:
we got rules like: Look for a file that size in that folder with parameters 1,2,3 (just an example, of course)
Now if the specified folder contains many files, every file has to be checked for the size, if there are many files of that size, every file has to be checked for the parameters. Each check takes time, that means: the more files, the more checks.
Win32.Qhost.ahnj rules contain many folders, many sizes. -> many checks, long time to scan.
I hope that helps understanding