If you've ever blocked a particularly annoying or abusive "friend" on Facebook, there's a chance they might recently have appeared back in your timelines.
That's because Facebook says there was a bug affecting about 800,000 users of Facebook and Facebook Messenger that unblocks people they had previously blocked.
"The bug was active between May 29 and June 5 — and while someone who was unblocked could not see content shared with friends, they could have seen things posted to a wider audience," Facebook said in a blog post. "For example pictures shared with friends of friends."
Facebook said 83 percent of the 800,000 users affected only had one person they had blocked temporarily unblocked.
It also didn't reinstate any friend connections that had been severed when they blocked that person (blocking a person automatically unfriends them as well), though someone who had been temporarily unblocked might have been able to contact the blocked person via Messenger.
Facebook said the bug has been fixed and temporarily unblocked friends are now blocked again.
Today's Top Stories
Those affected will get a notification on Facebook encouraging them to check their blocked list.
It's the second glitch in the space of a month announced by Facebook
.A few weeks back it asked users to review posts they'd made over a 5-day period in May, because a bug with its system turned some private posts public.