Facebook has admitted that a bug unblocked the blocked contacts of over 800,000 of its users.
The bug - now fixed - had hit user accounts between May 29 and June 5, according to the company.
The "issue has now been fixed and everyone has been blocked again," Facebook said in a statement.
It added that 83 per cent of Facebook users affected by the bug had only one person they had blocked temporarily unblocked and assured that the company was in the process of notifying the users, who were affected by the bug.
The Silicon Valley firm had also assured that the bug "did not reinstate any friend connections that had been severed."
The admission comes at a time when the company is already battling several privacy related controversies.
In March, Cambridge Analytica, a political-data firm was accused of illicitly harvesting and stockpiling data on millions of Facebook users to develop psychological profiles of voters that was allegedly sold, among others, to the company hired to run US President Donald Trump's presidential campaign.
The controversy led to Facebook founder Mark Zuckerberg being summoned before the US Congress and the European Parliament.
