The most useful software that is free to use (although you can give a donation) in detecting spyware, are;
spybot probably the best, with updates too (although you need to manually see if updates are available). Can also clean usage tracks (good if you share a computer with others), and some other features too. It also has other useful software, but for the more experienced computer user.
Next on the list is Ad-Aware SE Personal . This too is excellent at detecting spyware, and it also needs you to manually update the software). It has a customizable scan, and many more features, also you can add helpful plug ins.
Next is Spyware Blaster , which has a list of spyware, which blocks from downloading onto you computer….so you do not need to scan. It also has EULAlyzer 1.2 (January 9th, 2007).
Analyze license agreements for interesting words and phrases!
License agreements can be a pain and a bore, but not reading them can be dangerous. This has also proved useful.
Also microsoft defender which has been pretty good too, and can be auto updated.
Beware of some sites claiming to be helping to remove spyware and that are free, but are in fact harbouring spyware themselves and doing damage too your computer…..
For advice, see Counter Exploitation
All this freeware is not for commercial use, only for personal usage.