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 cannot 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.