Tone, different anti-spyware/adaware programs tend to have some differences in their "list of known threats". I've played with several of them, and some seem to pick up more things than others. As MS is a beta at the moment, some of the threats may not be in it's list yet, hence it doesn't recognise them as such. Some search bars that install themselves onto Internet explorer can be detected as spyware by certain software.
Wikipedia gives a good description
here