What's with the Yellow Blogs?

From time to time, I check the links to my posts on this blog. Quite often, one or more leads to a "blog" with a yellow stripe near the top, no topic, and posts apparently lifted at random from other blogs. I think I've seen other patterns too, some much less coherent.

My suspicion is that it's some kind of scam involving generating hits in order to sell ads, but the particular one I just looked at, although it says "ads by Google," doesn't appear to have any.

Anyone know?