That's not always going to be spyware, but if you're getting it when viewing this particular site, I have to say it probably is.
I know of numerous sites which pay for their bandwidth by allowing search engines to essentially buy the text that is posted on the site. Specific words or phrases are automatically converted to links that redirect you to said site's search engine.
This is how various websites support each other and the admistrators earn a living. By sharing "traffic."
I have never seen it on this site, however, and I don't think we ever will.