Please read the malware removal section on my website. (see my signature)
I believe it will make things more clear for you.
There is so many malware, that it is impossible for 1 application to detect it all.
Therefor there are applications that concentrate on 1 or a few kinds of malware.
Nowadays anti-virus software is basicly a wrong naming, they do not only detect virusses, but all kinds of malware.