The UN nuclear watchdog has acknowledged one of its former computer servers had been hacked.
Contact details for more than 100 experts working for the International Atomic Energy Agency (IAEA) appeared on November 25 on a hacker website, Parastoo, which is Farsi for the swallow bird.
In the posting, the hacker group called for the experts whose details were divulged to sign a petition calling for an "open" IAEA investigation into Israel's nuclear program.
The message also contained a threat to publish more personal information if the killing of Iranians linked to the country's nuclear program continues.
An IAEA spokeswoman Gill Tudor said the UN agency was taking "all possible steps" to ensure its computer systems and data were protected.
Israel is believed to possess nuclear weapons, although it neither confirms or denies this. Israel accuses Iran of secretly developing nuclear weapons, a charge Tehran denies.
Based on dpa, Reuters and AP reporting