Like you didn't see this one coming. According to some sleuthing by the Wall Street Journal, many popular Facebook apps – including titles from omnipresent game dev Zynga – are sharing your user ID with unauthorized third parties. The Journal found that "all 10 of the top Facebook apps transmitted user's IDs" – six of those apps, including Farmville at numero uno, are created by Zynga.
In addition, the Journal reports that "three of the top 10 apps, including FarmVille, also have been transmitting personal information about a user's friends to outside companies." Of course, your user ID is publicly available and is, by itself, just a number; however, this data can be (and, as the Journal reports is being) shared with other parties, specifically "at least 25 advertising and data firms." The Journal says that many devs may not have realized they were exposing that information – the referring page includes the user's ID in the URL. Whoops!
Facebook, for its part, says that mere knowledge of an ID "does not permit access to anyone's private information on Facebook" though some firms will pair IDs to whatever personal information is stored in a user's public Facebook profile. The company also says it will work to "contain the problem." A Zynga spokesperson said, "Zynga has a strict policy of not passing personally identifiable information to any third parties" and pledged to work with Facebook to "refine how web technologies work to keep people in control of their information." The way we see it, you've got two choices: 1) Stop using Facebook apps or 2) Resign yourself to a dystopian future wherein the entire world knows you play Farmville. How humiliating!