"The Federal Reserve system is aware that information was obtained by exploiting a temporary vulnerability in a Website vendor product," a Fed spokeswoman told Reuters. "Exposure was fixed shortly after discovery and is no longer an issue. This incident did not affect critical operations of the Federal Reserve system,"

The intruders appear to have gained access to a Fed database used to maintain contact with banks in the event of a natural disaster.

A Fed letter addressed to members of its Emergency Communication System (ECS) and obtained by Reuters warned that mailing address, business phone, mobile phone, business email and fax numbers had been published. "Some registrants also included optional information consisting of home phone and personal email. Despite claims to the contrary, passwords were not compromised," the bank said.

In a tweet sent out during the US Superbowl on Sunday, Anonymous claimed to have published the bank data as part of its OpLastResort campaign in protest against alleged government persecution of Internet whizkid Aaron Swartz, who committed suicide on 11 January.