A group calling itself the “Islamic State Hacking Division” has published a list of names with personal details of purported US servicemen, urging for their “brothers residing in America” to kill them. The unverified data breach is being investigated.

A source in the Pentagon said that the validity of personal information recently posted online is now being investigated, without commenting on the published threats.

“I can't confirm the validity of the information, but we are looking into it,” a US defense official, speaking on condition of anonymity told Reuters. “We always encourage our personnel to exercise appropriate OPSEC (operations security) and force protection procedures.”

ISIS hacking division asked its followers to kill military members 'wherever you find them' http://t.co/fAc9fzfYTdpic.twitter.com/7tSh3wfZ5f — slone (@slone) March 22, 2015

The Air Force rep told TV network The Blaze that they are reaching out to those listed in the document as their members: “The Air Force is cooperating fully with the DOD on this matter,” Lt. Col. Holly Slaughter said. “We are taking the appropriate steps to make sure that everyone who needs to know is notified.”

The so-called “Islamic State Hacking Division” took responsibility for the leak, claiming it hacked several military servers. It exposed the names and the whereabouts of alleged US military personnel asking for “lone wolf” attackers to kill those people in “in their own homes.”

READ MORE: Central Command Twitter account apparently hacked by CyberCaliphate

However, as NYT reported, quoting an unnamed Defense Department official, the information that was exposed most likely came from public databases and not the US military servers. The personal data on “kill list” could have come from news articles that at one point may have mentioned the servicemen by name.

It is not the first time that the ISIS internet hacking squad has staged an attack on the US government’s electronic resources. In January IS sympathizers took control of the US Central Command (CENTCOM) Twitter and YouTube accounts. Some reports suggest that the recent list could have been drawn up as a result of January’s hack.