( CNN ) A previously unknown group calling itself the Islamic State Hacking Division posted the names , photos and addresses of about 100 U.S. troops online , calling for attacks against them . Whoever created the file , posted online Saturday before being removed , claimed to have hacked military databases and said it was leaking 100 names `` so that our brothers residing in America can deal with you . '' The possibility of lone-wolf attacks in the United States , the type that this message calls for , is a threat officials take seriously . Attorney General Eric Holder said last month that the threat of a lone-wolf attack inside the United States is one thing that keeps him awake at night . But there was nothing to immediately validate the claims made by this unknown group . A Defense Department official told CNN that it can not confirm the validity of the online posting , but is looking into the claim . The FBI is also looking into it , a law enforcement official told CNN , adding there are questions about the credibility of those behind it . The Naval Criminal Investigative Service notified the Marines named in the file about this `` presently unverified threat , '' a Marine Corps spokesman said . The Navy reminded service members to make sure to limit the amount of personal information available online about themselves . The Army said in a statement Sunday that it was working with the Defense Department to `` determine the validity of any potential threats , '' and it echoed the Navy in advising soldiers `` to take prudent measures to limit the sharing of personal information online . '' A U.S. law enforcement official said that all 100 or so troops named in the file are being contacted . It is believed that ISIS members and sympathizers have been scouring social media sites trying to glean as much information as possible about service members , and have even threatened the spouses of military personnel online . The file appeared to include information that is already available publicly , through social media accounts , online phone directories and other accessible public records . In late November , the FBI issued a warning to U.S. military members that ISIS was calling for attacks against them , a law enforcement source told CNN . The source said that `` overseas based individuals are looking for like-minded individuals in the U.S. to carry out these attacks . '' The warning asked members of the military to `` review their online social media presence for any information that might attract the attention of violent extremists . '' The bulletin also said authorities were concerned that ISIS members were `` spotting and assessing '' individuals in the United States who may be interested in carrying out attacks inside the country against members of the military , a U.S. counterterror official told CNN . CNN 's Barbara Starr , Pamela Brown , Kevin Bohn and Mary Kay Mallonee contributed to this report .
An previously unknown group publishes a threat against U.S. troops . The Pentagon says it is investigating the threat.