For years, the U.S. military has pushed to meet prospective Generation Z recruits on Discord, the online group-chat tool where many spend their time. It even runs a 17,000-member chatroom there for service members to talk about first-person shooter games, meet with career counselors and participate in what one sergeant in 2019 called the "Army of tomorrow."

But Defense Department officials have also struggled to confront the risks of how Discord's closed channels operate - and the ease with which they can be used to expose military intelligence. Last month, in a detailed guide aimed specifically at Discord users, Special Operations Command, which oversees the country's most elite forces, told service members: "Don't post anything in Discord that you wouldn't want seen by the general public."

By then, hundreds of classified documents had already spilled onto a Discord server frequented by a 21-year-old National Guard airman, Jack Teixeira, who had used the government secrets, interviews and an FBI charging document suggest, to impress the teenagers and 20-somethings who'd joined the chatroom.

That attempt to flex his military status for online approval ended with Teixeira's arrest Thursday. On Friday, he was charged with two counts of retaining and sharing classified national defense information, punishable by up to 15 years in prison.

But the arrest doesn't end the dilemma for the military: how to supervise a young workforce that has access to classified secrets but lives much of its life online - including in corners of the internet where many share a fascination with military hardware and an eagerness to show off for strangers and friends. Two-thirds of U.S. military personnel are under the age of 30, with the vast majority of those under 25.

"Young men who may not feel their life gives them cachet and importance, they're trying to find that online . . . often by attaching themselves to the gravitas of war and combat," said James D. Ivory, a Virginia Tech professor who researches the social dimensions of online communities and video games.

Some of them, he said, seek to overcome feelings of isolation and gain clout with their peers by spending time in these small online communities where they may feel they can push the boundaries and build camaraderie - even though the groups offer only the illusion of privacy and control.

"We're seeing massive security breaches and potential global instability just because someone was insecure about their popularity," he added, "and wanted people to know they knew cool stuff about the military."

Video games are one of the most popular forms of media for the 18- to 21-year-olds who are the target for the Defense Department's recruiting efforts and make up much of its junior ranks. The military sponsors esports tournaments to drive interest and advertises on the popular game-streaming site Twitch.

Many gamers have flocked to Discord for its fast-moving mix of public and private chatrooms, known as servers, where members can exchange jokes, memes and voice clips in a place largely invisible to the open web. Founded in 2015 in San Francisco, Discord says its 19 million servers attract 150 million active users every month.

Teixeira's group first met up on a Discord server devoted to Oxide, a YouTube creator known for his gaming clips and detailed breakdowns of combat rifles, body armor and military loadouts. The server, like many on Discord, was frenetic and irreverent: A clip from 2020 shows the room devolving into a chaos of gunfire noises and shouts of "Allahu akbar."

A close-knit group from that server broke off into its own - named, for a pornographic meme, Thug Shaker Central - where they chatted about guns, games and geopolitics, and exchanged dark and racist jokes, members told The Washington Post.

Teixeira began sharing the documents late last year, FBI investigators said. By last month, a group member had reposted some of them in a separate Discord server, effectively sparking their viral spread.

In the offline world, Teixeira had worked in a relatively low-level IT-focused role as a "cyber transport systems specialist" in the Air National Guard, which gave him access to a computer network hosting top-secret information.

He worked at Otis Air National Guard Base in Cape Cod, Mass., far from the grisly realities of combat. When federal agents arrested him Thursday at his family home in the woody suburb of Dighton, Mass., he was dressed in gym shorts and a green T-shirt.

In the Discord server, though, Teixeira had built a devoted following as "O.G.," framing himself as a gun lover with a honed sense of combat strategy and intimate access to military secrets. A former Thug Shaker Central member told The Post that O.G. had shared the documents to educate his peers and build social capital on a slice of the internet where he was king.

Teixeira's profile on the gaming marketplace Steam shows him playing lots of first-person shooters and military simulations with millions of players: the realistic military shooter "Arma 3," the hardcore survival game "Project Zomboid" and the battle royale shooter "PUBG: Battlegrounds."

But he also inhabited a die-hard subculture attracted to the precise details of military weapons, technologies and strategies. His ability to use those secrets to gain him credibility within the group, members said, ended up becoming a temptation he could not ignore.

On the server, he talked openly about guns, Catholicism, libertarian politics, and the raids at Ruby Ridge in Idaho and in Waco, Tex., a common flash point for the anti-government fringe. He also posted video of himself firing a rifle while shouting racist and antisemitic slurs.

Though investigators said he used anonymous screen names such as "jackthedripper" and "excalibureffect," Teixeira proved, ultimately, not hard to find. In a charging document Friday, an FBI agent said his Discord account information, which the San Francisco-based company provided to authorities, had included Teixeira's real name and home address.

That kind of online bravado is common in Discord gaming groups steeped in the macho, hard-charging culture of tactical shooters and military combat, Ivory said. Some members end up egging each other on toward increasingly cavalier behavior, he said, often because they feel safer in a closed-communal setting than if they were broadcasting their feelings to social media or the world.

That lack of discretion, he said, has led some members to adopt increasingly radical attitudes and behaviors. That's a potential risk for young service members, he said, particularly those who enlisted with expectations of combat duty but ended up working a job that now plays out largely on a screen.

"Some people may join the military because of the allure of the warrior ethos, and they may not feel very validated sitting in front of the computer all day," Ivory said.

Discord said in a statement that it is cooperating with law enforcement and declined to comment further. The company said it scans for violent and other rule-breaking content but also depends on volunteer moderators to flag potential threats, probably allowing some risks to go unseen.

In a report by the House select committee investigating the Jan. 6, 2021, attack on the U.S. Capitol, Discord officials were said to have acknowledged that "the risks of relying too much on user moderation when the userbase may not have an interest in reporting problematic content."

The Defense Department, facing a recruiting shortage, has nevertheless adopted a nationwide strategy of using gaming and online culture to attract new troops, many of whom grew up with Xboxes and iPads and who live much of their lives online.

Nearly every service branch now has an esports team that competes on first-person shooter games such as the Halo franchise and "Valorant," some of which have their own private Discord servers where service members can chat.

Military esports teams also participate in nationwide competitions and stream their gameplay on Twitch. The Army's esports Discord server welcomes active-duty Army and National Guard members, as well as contractors, veterans, and their families and friends, encouraging them in a welcome banner to "be all you can be."

Progressive activists have criticized the military for using Twitch streamers and gaming channels popular with young viewers to promote military life and shape their perceptions about war.

Rep. Alexandria Ocasio-Cortez, D-N.Y. sponsored a House amendment in 2020 to ban the military from using Twitch to recruit that did not pass. "War is not a game," she said on Twitter. "We should not conflate military service with 'shoot-em-up' style games and contests."

But Amy J. Nelson, a technology expert and foreign policy fellow at the Brookings Institution, said the Discord leaks reflect a broader challenge of how to block the sharing of classified information.

Discord is "a tainted concept now," she said. "Does the Pentagon still use it? Does it use it officially? Does it use it unofficially?"

The Pentagon's detailed guide to Discord shows military officials counseling users to be aware of "personal security vulnerabilities" and suggests specific privacy and safety controls for an app that it said allows "friends and communities to stay in touch and spend time together."

"It may be a private server," the guide says, "but conversations and photos/videos can be captured by screenshot or recorded and leaked."

The military command has also published similar guides to Twitch, TikTok, and the dating apps Tinder, Bumble and Hinge, among other apps, recognizing that people in their 20s and younger are likely to be unwilling to give up online habits they've held for a lifetime.

The TikTok guide doesn't even discourage using the popular short-video app, which is banned on military devices but allowed for personal use, though it does recommend settings and guidelines that could limit the risks of an app owned by a Chinese firm.

Roughly 3 million Americans have undergone the months-long process of acquiring security clearance, where they are asked about details of their behaviors and personal histories and made to provide names they might use online. But many Discord servers are invite-only and ask for direct confirmation of members' authenticity, blocking them from public view.

President Biden said in a statement Friday that he had directed the military to "further secure and limit distribution of sensitive information." Defense Secretary Lloyd Austin said Thursday that he had ordered a review into the Pentagon's intelligence controls and reminded anyone with classified access that they had "a solemn legal and moral obligation to safeguard it."

The leaks could amplify calls in Washington to more closely monitor chatrooms and social media. Such a measure is not unheard of: Undercover governmental investigators have in the past closely monitored jihadi forums organized by Islamic State and al-Qaeda militants for the purposes of investigation or intervention.

But civil liberties advocates have argued such tactics could violate Americans' First Amendment rights of free expression or their Fourth Amendment protections against unreasonable searches.

"We do not have nor do we want a system where the United States government monitors private internet chats," Glenn Gerstell, the former general counsel of the National Security Agency, told NBC on Wednesday.

On Discord, some servers already joke about the possibility of being surreptitiously infiltrated by the government. Using a word first coined on the anything-goes message board 4chan, people commonly accuse others of being "glowies" - federal agents whose out-of-place behaviors are so obvious that they practically glow.

But surveilling gamer chatrooms might also end up pushing away the same young recruits the military desperately needs, all for questionable practical gain: The internet is full of ways to anonymously share images, videos and documents.

Before the Discord leaks, similar breaches had played out on the official message board of the ultrarealistic combat game "War Thunder," with users from around the world divulging secret information about anti-armor shells and attack helicopters.

One message board poster, who claimed to serve in a French military unit, uploaded a classified manual in hopes of winning an argument about the turret rotation speed of a Leclerc S2, one of the nation's main battle tanks.

Jordan Uhl, a progressive activist who has criticized the use of Twitch for recruiting, said the military's heavy advertising through video games and Discord chats could end up backfiring by attracting young people with a "warped impression" of military life.

"This is a new challenge for the military: When you have all the people who grew up in a purely digital age enlisting, the lines are blurred for how they communicate," he said.

"People are growing up playing military videos and consuming military propaganda through YouTube in ways prior generations never experienced," he added. "The way they're recruiting and the places they're recruiting, the military is going to get more people like this."

The Washington Post's Aaron Schaffer, Pranshu Verma and Taylor Lorenz contributed to this report.