The Federal Reserve acknowledged Wednesday its computer systems were accessed by hackers but said the incident did not affect the central bank’s “critical operations.”

The acknowledgement came days after the hacker group known as Anonymous claimed it had posted personal information of some 4,000 bankers, purportedly obtained from the Fed.

“The Federal Reserve System is aware that information was obtained by exploiting a temporary vulnerability in a website vendor product,” a Federal Reserve spokesman said in a statement in response to an AFP query.

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“The vulnerability was fixed shortly after discovery and is no longer an issue. This incident did not affect critical operations of the Federal Reserve System.”

On Monday, an Anonymous-linked Twitter account called Operation Last Resort, claimed in a tweet to have obtained and posted “4k banker d0x via the FED.”

The group argues it is taking actions responding to the suicide last month of Aaron Swartz, an Internet freedom advocate who was being prosecuted for illegally downloading millions of academic journal articles he had allegedly planned to distribute for free.

“This tragedy is basis for reform of computer crime laws, and the overzealous prosecutors,” the Twitter account states.

The incident comes after the US Department of Energy confirmed it was the target of a cyber attack in January, which stole employee and contractor data.

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The news also comes after revelations of high-profile cyber-attacks targeting US news media including The New York Times and The Wall Street Journal said to be originating from China.