Many of Facebook's most popular apps are sharing user data with third parties, according to a Wall Street Journal report.
The paper's investigation has revealed that all ten of Facebook's most popular apps, including Farmville, Texas HoldEm Poker and FrontierVille, are grabbing a user's ID number, which can then be passed on to third party advertisers.
With 59 million players of Farmville alone, enormous numbers of users are affected.
These third parties can then cross-match the information with public data such as census information to build detailed profiles of individual users.
Possession of a user's unique ID allows a company to look up that user, even if privacy settings are set at their tightest.
According to the WSJ, the apps are sending the information to at least 25 external organizations. It says that one data-gathering firm, RapLeaf, harvested user IDs and linked them to its own database, which it sells. RapLeaf claims this was a mistake.
RapLeaf also sent the Facebook IDs it harvested to a dozen other companies.
The privacy hole clearly violates Facebook's terms of service, which state that third party apps are barred from providing user data to third parties, with or without a user's consent.
Facebook says it's reviewing the WSJ report, but says it accepts the breaches are happening and will work to fix the problem. Several of the offending apps seem to have been shut down already, including Gift Creator and Quiz Creator from LOLapps.