<cynical interpretation> The data can be retained so long as Facebook is in the business of targeted advertising, and that's "the purpose for which the information was obtained".

Also, I'm now looking forward to Zuck's next apology for "a breach of trust" and his explanation of how they "failed to live up to their own standards" when it becomes publicly undeniable that their "Full and irrevocable anonymisation" of data they've claimed is deleted is as flawed as all the other attempts we've seen of doing that.