Facebook said it is investigating a glitch which has seen some users' group memberships reactivated after they had been canceled.
One administrator of several private groups on Facebook was concerned that old members would be able to access "highly sensitive" information.
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"Am an admin on several secret/private groups on facebook with highly sensitive info. This morning all old members (from 5 years) were added," Carrie Cutforth Young tweeted.
According to BBC News, others have complained of having to leave groups, one-by-one, all over again.
Those affected have seen notifications from groups that they had been subscribed to when they were nowhere near a computer or internet-connected device, reported the Next Web. Some were even added to more than 250 groups that they had to manually unsubscribe from. Private group administrators have also seen members added without permission, while others have had banned users regain access to discussions they had been restricted from seeing and participating in.
Facebook has assured users that the glitch would not breach their privacy or give anyone access to their personal information if they had already hidden it via the site's privacy settings, noted the Daily Mail.
"Some users appear to have been re-added to groups that they have left in the past," Facebook said in a statement to BBC. "We are investigating the issue."