Slashdot is reporting that Facebook has filed a patent application (titled "Communicating Information in a Social Network System about Activities from Another Domain") that describes methods for tracking Facebook users while they're on other sites.

I've not yet read the patent app (it's long). It's a priority claim incorporating a provisional application filed in February of last year. The new application cites no prior art at all, which strikes me as slightly odd; perhaps that's in the provisional app.

The gist of the application appears to cover the techniques that are behind the Facebook "widgets" - content on Web pages that can access your Facebook-created cookies even after you've logged out of Facebook itself. Thus your movements across the Web are reported back to Facebook and you get ad-served (also described in the patent application) based on the knowledge of who you are that Facebook has accumulated.

Also of interest (and noted in other blogs) is that the patent never says (nor is it assigned to) Facebook. Usually a patent application is filed with the inventors names on it, and then some form of assignment statement. Particularly in the high-tech industry it's standard practice for employees to sign agreements at the start of their employment that any intellectual property they come up with during business hours or that relates to the business of their employer is to be assigned to their employer. No idea why such a statement would be absent from this application.

It's probably worth noting for the record that Facebook has made claims to the effect that it does not track logged-out users, claims that are widely seen as... what's the word I want here... bullshit. See for example, Dave Winer's column titled "Facebook is Scaring Me".