A 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.
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.
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.
One military wife recalls recently staying up all night and deleting every Facebook picture of her children, every post that mentioned them or where they went to school. She Googled herself, trying to figure out how easy it would be to find where the family lived. In the morning, she went to her car and scraped the military decal off the front window.
As the spouse of a Special Forces soldier, she's always tried to be conscious of how much she advertises that she and her three young children are a military family.
"It's hard because I am so proud of what my husband does, but lately so many spouses that I know are actually scared that they could be targets of ISIS or someone who sympathizes with ISIS," she told CNN in January, asking that CNN keep her name out of the story for that reason.
Pro-ISIS hackers have never been responsible for a major cyber breach but some experts worry their capabilities are growing. J.M. Berger, co-author of "ISIS: the State of Terror," told CNN, "There are indications some former members of Anonymous and TeaMp0isoN (another hacking group) are now hacking on behalf of ISIS."
The large majority of those within such hacking collectives are thought to hold very different views. In the wake of the attack against the Charlie Hebdo satirical magazine in Paris in January, hackers affiliated with Anonymous declared online war on ISIS and al Qaeda.
Regarding this weekend's threat targeting troops, the Naval Criminal Investigative Service notified the Marines named in the file, a Marine Corps spokesman said. But the spokesman told CNN that the threat has yet to be verified.
The Navy reminded service members to limit the amount of personal information they share online.
On Sunday, a Defense Department official told CNN that it cannot confirm the validity of the posting of troops' information, but said it is investigating.
The FBI is also looking into the post, a law enforcement official told CNN, adding there are questions about the credibility of the person or persons who posted it.
In January, military families were spooked by an online message on Central Command's Twitter account
which was in all caps.
It read: "AMERICAN SOLDIERS, WE ARE COMING. WATCH YOUR BACK. ISIS."
The tweet included a link to a statement that said, in part, "We won't stop! We know everything about you, your wives and children. U.S. soldiers! We're watching you!" The Twitter hacker managed to post other threatening messages, propaganda videos and some military documents until the accounts were disabled.
Central Command quickly made public assurances that it was relatively easy to hack Twitter, no serious security details were revealed and it would find who was behind the hack.
Army wife Ashley Broadway-Mack said the messages just amplified the anxiety she already feels after recent terror attacks targeting military personnel, law enforcement officers and civilians.
She and other family members told CNN in January that they first began to think about the possibility in May 2013 when a uniformed British soldier in London was murdered by two men who shouted "Allahu akbar," or "God is great."
Others started to fear the possibility of their service members or themselves being targeted after the killing of a Canadian soldier during an October attack on the country's Parliament. Attacks and plots in Australia have them concerned, too, they said.
In September, the Australian Prime Minister said a plot to kidnap a member of the public, behead the victim and then drape him or her in an ISIS flag
had been thwarted. In December, a self-styled Muslim cleric held hostages in a Sydney cafe
for 17 hours, a drama that ended with the deaths of two hostages. The gunman, who was known for sending hate mail to military families, was killed.
The slayings in Paris, for which al Qaeda in the Arabian Peninsula has taken responsibility
, have prompted Broadway-Mack to think about security at North Carolina's Fort Bragg.
"Before the incident in Canada, I honestly didn't think ISIS was a threat to our family or other military families," she said in January. "I worry about the hundreds, thousands of folks going to and from work in uniform. They, too, could be targets. I think of other areas around the country where there's a large military presence -- an attack, ambush, lone terrorist is something I fear.
"I hate to say it, but I honestly no longer think if, but when and where," she said. "I think it's only a matter of time."
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.
Not giving in
, who is married to a commanding officer, told CNN in January that she she knows military members and spouses who have stopped openly carrying their uniforms to their car after a visit to the dry cleaners.
Some have stopped wearing clothing with military insignia and are more careful when they open their wallet to avoid showing military IDs or payment cards.
The small, simple changes don't mean military family members are running scared, Volkman said.
But it was difficult when her young daughter was watching television and saw the news about the Centcom hack and the threat that ISIS was coming for soldiers.
"She turned and looked at me and you could see it registering -- we're soldiers. She had a very worried look," Volkman said. "But kids are comforted by whatever their parents tell them. We can't live our lives in fear and we try to reassure them."
A blogger and communications firm CEO, Volkman wondered how she would even begin to scrub her online presence. Angela McCormick Ricketts
also said in January that she's thrown her hands up about the matter of online privacy.
Her memoir, "No Man's War"
is a critical success. She's done a lot of press and is omnipresent online.
"I'm probably screwed if ISIS starts targeting yappy military spouses, so it's too late now! There's also a part of me that thinks that's what they want -- to make us always looking over our shoulders. So no. No to all of it," she said.
It's a matter of principle, she and others said.
Why should families bend to fear and stop sharing online when social media has helped many of them get through 14 years of nonstop war?
Though the military has at times struggled with how much freedom
its members should have
on social media,
relatives have wholeheartedly embraced it.
Military families appear to use social media at higher rates than civilians, according to data from the Pew Research Center
. Social media as we now know it wasn't even around when the Afghanistan war began
. Facebook launched in 2004, almost exactly a year after the United States invaded Iraq. Now, dozens of military spouses have blogs and Facebook caters to the community.
A 2014 survey
by military advocacy group Blue Star Families
found that 75% of 6,200 respondents considered the use of social media to be very important.