Facebook has announced the discovery of a new bug that seems to have temporarily removed blocked profiles from approximately 800,000 users' block lists. That's according to a post on the company's blog which confirms that the problem is now fixed. The bug was 'active' for nearly a week, between May 29 and June 5, and allowed those users to see content shared with friends of friends. The bug did not go so far as to add those users back to affected accounts friends list. Blocking a friend will automatically remove the account from a user's friends list if they two accounts are joined when the block occurs. That wasn't reversed in this case. In the meantime, as many as 83-percent of affected Facebook users only saw the unblock applied to one previously blocked account. So the bug wasn't clearing people's block list entirely. However, it did allow blocked users to establish contact again via messenger.
With that said, the fix isn't necessarily complete either. Facebook will be sending out notifications to affected users in order to ensure that they check their own lists for any anomalies. Those users who are being notified appear to be receiving the names of accounts that were temporarily unblocked as well. That should at very least make it easier for users to see how seriously the bug may have affected them at an individual level. Since users block one another for a variety of reasons ranging from annoyance to harassment and threats, it may be a good idea for all users to check that their lists are intact. No technology is perfect and it is always possible that Facebook has missed an account or two in their investigation.
Facebook has not revealed the underlying cause of this particular bug or provided any insight with regard to whether it affected predominantly web or mobile users. Regardless of what the fault turned out to have been, the problem only seems to have affected block lists for now. In the meantime, the company is asking users to review its guidelines for staying safe on the social network, including how to handle harassment and bullying.