antispywares ≠ antivirus. You need both kind of programs.
AdAware and Spybot are antispywares. Spybot is pretty decent. You can also try Microsoft's WindowsDefender (formerly Antispyware).
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http://www.microsoft.com/athome/security/spyware/software/default.mspx
Good free antivirus are Avast! and Clamwin.
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http://www.avast.com/eng/download-avast-home.html
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http://www.clamwin.com/
Whatever you do, don't buy Norton products, they'd just make the matters worse, don't think your software will protect you if you take risks, make backups, and allow the antispyware and antivirus to auto-scan and auto-update.