"Now we have your attention America," the hacker group posted to Twitter Sunday, adding in a separate message, "We have posted over 4,000 US bank executive credentials."
The Twitter post linked to a spreadsheet - which has since been removed - containing usernames and personal contact information for bank executives across the US.
The document was quickly shared across various social media accounts affiliated with Anonymous.
The information was obtained from the Emergency Communications System database belonging to the Federal Reserve Bank of Saint Louis, the tech website ZDNet reported Wednesday.
A spokesperson for the Fed confirmed the breech, but downplayed the severity.
"Information was obtained by exploiting a temporary vulnerability in a website vendor product," a spokesperson for the US Federal Reserve told the Huffington Post, adding that the problem was "fixed after discovery and is no longer an issue."
According to the spokesperson, who asked not to be identified by name, the breach "did not affect critical operations".
Anonymous said the attack was part of its "Operation Last Resort" campaign, an effort to reform computer crime laws and what the group called "overzealous prosecutors".
The Federal Reserve attack was the latest in a string of cyber hacks by so-called "hackivists" that began shortly after Internet activist Aaron Swartz committed suicide in January as he was being prosecuted for violating the Computer Fraud and Abuse Act.
US Federal authorities had charged him with hacking and downloading articles from the academic journal JSTOR, but dropped the charges shortly after his death.
Last week, as part of the operation, Anonymous hacked the website of the US Sentencing Commission, a group that creates and establishes sentencing guidelines and policies for federal courts.
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