[Mattylad]

It's best to use these in conjunction with each other as they all seem to do slightly different things.
Spywareblaster prevents them getting opn your PC in the first place, you must check for & update them all regurally.

Scansoft search & destroy also does this & can scan the PC for them.
Adaware also scans the PC & is not memory resident so needs to be done regurally.

There is also a utilty called "hijack this" that will scan for registry keys that are used by trojans etc to hijack your PC.

Getting them all & making a point of using them on a regular basis is the key, it takes a little effort to keep them away but is worth it in the end because you are rewarded with a crud free PC that runs when you need it to.