My Computer builder put me unto Panda Antivirus several years ago and it has performed flawlessly. It now includes a great firewall.
Trend Micro also offers a super spyware finder. It is the best I have used and often finds things that my "paid for " Spy Sweeper misses.   
http://www.trendmicro.com/spyware-scan/
Trend also has a free antivirus scan that my local shop uses as an excellent everday tool. Go to home page for the virus scan.
(Google...Trend Micro)