A lot of the popups are from so called free ware or more like it ad-ware. You download a utility or program like "Kazaa" (sp)or "Morpheus" (sp), and by installing them you agree to let them put files and/or adservers on your computer. In some instances you are sharing files and folders to the internet for other to download from. (music, videos, etc) some of the have small utilities that lets the internet know your computer is back on and online (tnkrbell.exe) others keep track on you on and off line (keystroke logging)....
This is just the tip of the iceberg.. as all IT people out ther know. Be careful and stay away from free (adware), lavasoft is a GOOD company. If you have problem downloading from the usa site (asking for info etc) try the
www.lavasoft.de site.
Nils