Yep, you've got some kind of "targeted marketing" spyware that automagically infected your box. Yet another way for someone to manipulate a Windows box for a quick buck.Some sites highlight certain terms - I can think of reviews on cartalk.cars.com for example. I've seen text there highlighted in Opera on Linux which I use, and I know that there's not a chance I have any spyware. So, you could highlight sections of your site in the HTML code, to emphasize something for your viewers. But, since you're also getting links, I don't think that is the case.I think a malicious app is running in the background, picking out certain strings of text in the document, and manipulating your browser to add the highlighting and links.You may want to go out and get something like Spybot Search and Destroy.
http://www.safer-networking.org/ It is available free of charge, and does a pretty decent job at removing that garbage. Alternatively, there are many others, such as Adaware, etc. that you could try. Let us know if you need any help getting this stuff off your box!