as Bring It On says, those popups themselves are the infection.
You should also install a popup blocker, if you don't already have one on your system. Unless it is old software, your browser should have one built in. Take a look and see if maybe you have it disabled.
All the free software mentioned is good stuff... i can also recommend these alternatives that i have used myself.
Firewall - Zone Alarm has always been my fave, and it's latest incarnation is really really good. Take a moment to read through CNET's review..
download.cnet.com/ZoneAlarm-Free-Firewal...0435_4-10039884.html
for anti virus i like AVG which is free for personal use.. very easy for non techies to understand and use, and updates itself daily with no fuss, keeping you well protected from all the latest bugs. It is the number one CNET antivirus download, beating second placed Avast by almost half a million downloads..
download.cnet.com/AVG-Anti-Virus-Free-Ed...2.html?tag=mncol;pop
for removing any issues you already have.. you can try Trend Micro's 'Housecall' which is thorough and non invasive to your system... I always rexcommend it to friends with problems, and all have been happy.
housecall.trendmicro.com/uk/
for malware/adware/spyware protection, spybot search and destroy is excellent, and has a cool name!
www.safer-networking.org/en/index.html