Browser Spyware: Watching Where You Linger

An Anonymous Coward writes: "Just when you you'd installed Junkbuster and thought it was safe to go back onto the web, the BBC runs this story which tells you that webshites will soon(?) be able to tell whether you are reading the page, what parts of it are of interest to you, etc. Guess we can expect porn sites to be the first to take advantage of this." Or perhaps someone else is already doing this, and hasn't told you.