The contact details of more than 100 scientists associated with the Vienna-based group appeared online several days ago, according to an IAEA spokesperson late Tuesday. The agency said it was investigating the breach.
"The IAEA deeply regrets this publication of information stolen from an old server that was shut down some time ago," IAEA spokesperson Gill Tudor said.
The hacker, or hackers, using the Iranian name "Parastoo," called on the scientists to investigate Israel's nuclear program.
The Israeli government has neither confirmed nor denied having nuclear weapons.
Accusations relating to Israel and Iran's nuclear capabilities have only deepened the enmity between both sides. While western nations have imposed sanctions on Iran as an admonishment for its alleged development of a nuclear weapon, no such sanctions have been imposed on Israel.
The hostile situation has led both countries to accuse the other of assassinations. Earlier this year, Iran pointed the figure at Israel and the US over the death of one its top scientists. Soon after, Israel blamed a series of assassination attempts on officials abroad - including a magnetic bomb in New Delhi - on Iran.
"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-favored element entertains another sip of motorbike & magnet bomb cocktail," Parastoo said in its message online, according to news agency DPA.
kms/ccp (dpa, dapd, Reuters)