Spywares are automatic programs that collect user information. Spyware can be developed by companies that want to monitor users and then sell data over the internet.
Another way to catch it. Spywares is through viruses that intend to steal certain data from users.

Spybot – Search & Destroy is a tool that allows detecting and removing spyware. Spybot-S&D is a free tool.

Highlight in this version for "official" support to Windows Vista.