I've spent the morning scrubbing my two laptops to get back to normal. Maybe this can save someone a few minutes.
In your browser, there may be extensions that have been loaded, or under Control Panel Programs there could be added programs on your computer. These skunks sneak into your quiet world when you download something from the Internet, even from reputable suppliers if you do not go to the trouble of making a custom installation. They cause those dumb double-green underlines or nuisance pop-up as you try to browse.
Extensions can be disabled or trash-canned. I'd trash can them unless you are clear about what they do. For example, Norton adds a security extension that I leave active.
Invading programs require going to Control Panel/Add Remove (WinXP), Programs and Features (Win7) or similar (depending on your version of Windows). You can sort by installation date. Look for anything recent (within the last month). There may be some valid programs that you intentionally installed, with this unwanted crap installed on the same date. In Win7, right click and Uninstall.
There can certainly be stuff deeper hidden than can be simply uninstalled, so make sure to keep your security software current. I use Norton and have been very happy with it.