Contact details of international scientists from a computer server of the International Atomic Energy Agency have appeared on a hacker website, the agency confirmed Tuesday in Vienna, DPA reported.
The message posted online Sunday contained a threat to publish additional personal information if the roadside bombings that have killed several Iranian nuclear scientists continue.
"We are reassuring IAEA that their critical information is safe with us as we are brothers. However, we can not guarantee the same if a Western-favoured element entertains another sip of motorbike & magnetbomb cocktail," said the message by one or more hackers going by the Persian name Parastoo.
Tehran has accused Israel and Western governments of having attacked its nuclear experts.
IAEA spokeswoman Gill Tudor said that her organization's IT experts were investigation the data breach.
"The IAEA deeply regrets this publication of information stolen from an old server that was shut down some time ago," she said.
A source following the incident told dpa that it was unlikely that official Iranian entities were behind the IT attack: "It was too ham-fisted to be the official effort on behalf of a government."
The message on the hacker site made a reference to the computer virus Stuxnet, which experts believe was developed by Western intelligence agencies to harm Iran's nuclear installations.
The hacker or hackers called on the physicists on the IAEA list to petition for an IAEA probe of Israel's nuclear programme.
The email addresses of the exposed scientists were likely stored on the server because they attended IAEA events, the source said. The scientists are not related to the IAEA's Iran investigations, he said.