US officials are claiming that the Federal Office of Personnel Management and the Interior Department were hit with a massive hack and some four million personal records could have been stolen, according to the Associated Press.
The incident occurred in December was only discovered in April.
The administration of President Barack Obama is investigating the breach and trying to determine the extent of the hack, according to a congressional aide who wished to remain anonymous.
At this time it is not clear how much and what sort of information was stolen, though the breach is said to affect millions of present and former government workers.
The White House is expected to hold a briefing on the hack late Thursday or early Friday.
According to the Wall Street Journal, US officials suspect that China is behind the breach, calling it one of the largest thefts of government data ever seen.
The Office of Personnel Management acts as the human resources department for the US government and holds troves of personal information. The department also issues security clearances and conducts more than 90 per cent of federal background investigations.
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