I've used Spybot for a couple years now - good program.. I use that, and Hijackthis which is also a great program (although you gotta kno what you're doing), and never have any problems..
A tip alot of people don't realize with these scanners - for best results, use them in Safe Mode, by rebooting your computer, and tapping F8 until you get the menu to select Safe Mode.. Reason being, if you have spyware/malware on your computer, it's already running which makes it harder if not impossible to remove.. The scanners will usually have you reboot to finish the cleaning, but you're just much better off running the program from Safe Mode initially.