Some female Marines were sent screen shots of nude and private pictures of themselves from concerned colleagues. A few would get texts from their friends alerting them to what was online. Others found vulgar messages from strangers in their inboxes.

The red flags were different, but the revelation was the same: Their intimate photos had been shared online without their consent.

Marine officials on Sunday said the branch was looking into a number of Marines, as well as current and former service members, who shared naked and compromising photos of their female colleagues on social media through a shared drive on a Facebook group called Marines United.

The incident has prompted an outcry from senior Marine leaders and an investigation by the Naval Criminal Investigative Service, but according to nine current and former female service members, online harassment goes well beyond a single shared drive or Facebook group.

The behavior has become pervasive in the younger enlisted ranks throughout the Marine Corps, threatening unit cohesion at the lowest levels and its ethos at the highest.

The existence of the shared drive was first reported through the website Reveal, in conjunction with the War Horse military news website.

Many of the women who spoke to The Washington Post did so on the condition of anonymity because they fear reprisals from fellow service members and their chains of command.

The Marine’s highest ranking officer, Gen. Robert Neller, wouldn’t comment on the specific investigation but called the reported postings “distasteful.”

“I expect Marines to give their all to be the best human beings, teammates, and Marines possible,” Neller said in a statement.

Women who have experienced the public shaming firsthand take a starker view.

“It’s Marine Corps wide,” said Marine Pvt. Kally Wayne, 22, who joined in 2013 and was removed from the service three years later for disciplinary problems.

In early 2016, her ex-boyfriend, a Marine, posted a sex tape they had made in 2013 to a Marines Facebook group, which quickly spread, eventually getting posted on Marines United, which has 30,000 members, where it appeared sporadically.

“I went to the police to get them to take it down and they told me because I didn’t live in North Carolina they couldn’t do anything,” Wayne said. “I went to his command and they said, ‘Why don’t you not make sex tapes?’?”

Wayne said she knows at least 10 other women who have endured online sexual harassment. She said that a meme of her had already appeared on another group after Marines United was taken down after the War Horse article.

It is hard to trace where the Marine Corp’s online culture of illicit photo-sharing began.

With about 7 percent of its 200,000 strong active duty ranks made up of women, female Marines are vastly outnumbered by their male counterparts.

In 2013 and 2014, the Marine Corps Times and the military website Task and Purpose wrote stories about the Marine Facebook group called Just the Tip of the Spear, commonly known as JTTOTS.

The group bills itself as a hub for “some of the camaraderie” that veterans miss after they leave the service.

“I don’t know how we got here,” said one female Marine whose pictures also appeared on the Marines United group as well other pages and Tumblrs. “A couple years ago, it was just people making fun of other Marines messing up online, now it’s this.”

Just the Tip of the Spear, like many other Marine Facebook groups that have at one point or another displayed inappropriate pictures, has been taken down numerous times only to reappear in different incarnations.