Social networking giant Facebook has taken action against known developers selling user names and contact lists.
User details were being sold to data brokers, enabling them to use the information to target adverts more acutely.
Facebook uncovered these sales while investigating a web browser bug that allowed user IDs to be shared inadvertently.
The developers, less than a dozen, that have been caught have now been banned for six months from connecting to Facebook. Their identities have not been revealed.
However, ad-targeting firm Rapleaf were named as one of the data brokers which have been purchasing UIDs. They have reached an agreement together whereby Rapleaf's involvement with any Facebook applications has now ended.