The military is warning about 100 service members about an online threat by a group purportedly affiliated with ISIS that has posted their alleged personal details and called on sympathizers to take violent action against them.
U.S. officials say the military services are notifying the families of the individuals named on the list.
On Saturday, a previously unknown group identifying itself as the "Islamic State Hacking Division" posted on a website the names, photos and home addresses of 100 American service members it said were involved in the U.S. airstrike campaign against ISIS in Iraq and Syria.
It said it did so to enable lone wolf sympathizers to kill those named on the list.
U.S. officials said they were aware of the list and were looking into it.
"I can't confirm the validity of the information, but we are looking into it," a Defense Department spokesperson said. "The safety of our service members is always a concern."
A law enforcement official told ABC News that the FBI is aware of the post and "monitoring" the situation.
Defense officials said the military services were contacting the families of the individuals included on the list.
"The Air Force is cooperating fully with DOD on this matter," Air Force spokeswoman Lt. Col. Holly Slaughter said. "The Air Force is taking the appropriate steps to make sure that everyone who needs to know is notified. As always, force protection is a primary concern."
"Naval Criminal Investigative Service is looking into the matter for the Navy and is taking the appropriate steps to ensure that everyone is notified," said a defense official.
Marine Corps spokesman Lt. John Caldwell said NCIS is conducting in-person notifications to the Navy and Marine personnel regarding the currently unverified threat/data breach.
"It is recommended Marines and family members check their online/social footprint, ensuring privacy settings are adjusted to limit the amount of available personal information," Caldwell said. "Vigilance and force protection considerations remain a priority for commanders and their personnel worldwide."
The hacking group claimed it compiled the list from military records, but it appears the photos and information may have come from information available on social media sites or public records. Some of the names appeared in official Defense Department articles about the war on ISIS or other unrelated operations.
Over the past year the military services and regional commands have taken steps requesting its personnel be prudent and limit the amount of personal information posted on social media sites.
ABC News' Mike Levine contributed to this report.