Systems and needs and some wants vary due to variables. Various variable that vary due to well..... variabilties.
Old Coot generally recommends AVG anti-spyware and Nod32 anti-virus along with implementing safe surfing practices and setting up thine e-mail reader to minimize infection via that route.
AdAware is good and is used along with Spybit Search and Destroy and the Comodo firewall.
Spyware Blaster also has a nook within my security set-up.
Opinions as to what optimizes a safe crud-free system varies among members of the human species.
As the neighbor above proclaims, steer clear of programs that declare your electronic brain is..... INFECTED!!!!!! EEEEEEEEK!!!!!!! And then want thee to buy their product. Too often the so-called infection does not exist.
In your case you may be infected and need to take the needed steps to oust that rascally varmint. But, it's best to stop the infection from the get-go.
Another place to learn about your possible infection:
http://www.wilderssecurity.com/index.php
Many places to obtain advice and guidance, not all equally as good.
Whatever thou doeth.... ensure hostile coding is removed, that is, if any actually is present; then.... do what is needed to keep the bad guys at bay.
Free products can work and work well. However, there are times when the cost for quality is well-worth the price.
At the least, ensure you have a good anti-virus.
And, look for a safe surfing guide so you can set thine machine up properly to avoid infection.
Of course, you may have already done everything required already so this advice is meaningless. That's okay. I'm used to that. Computer security is much akin to my love/sex life. Meaningless. Well, unless infected.
Ewwwwww!!!!!!!!!!!!!! INFECTED!!!!!!!!!!!!!!!!!!!!!
Ahem.
Don't worry, even the most proficient computer folks get infected time to time.
Good luck!!!!!!
