Mac, I dont trust MS either, however ....
I have just tried the Microsoft AntiSpyware and at first impression it seems to work OK.
Although it does ask you to submit your OS key before downloading, it is not compulsory to do so.
The program itself is a bit Adawareish and simple to use.
Before using the program, I updated Adaware, Spybot, Spyware blaster and CCleaner then ran these programs to ‘clean the puter out.’
I then ran the Microsoft program (Deep scan) and it came up with 4 threats.
1. Bridge/Winfavorites (spyware) and was rated as a severe threat.
2. PowerReg Scheduler (spyware)
3. MoneyTree (Dailer) severe threat
4. SearchSquire (Adaware) elevated
It suggests options for dealing with these spies which I used for removal.