A man using his mobile device passes a portrait of Mao Zedong in Beijing. Mobile device usage and e-commerce are in wide use in the Chinese capital despite serious restrictions on Internet access. (Michael Robinson Chavez/The Washington Post)

He first started circumventing the Great Firewall to access pornography. Back in 2003, when he was in college, it was pretty easy: Access some proxy servers, and away you go.

More than a decade later, he has become an IT professional and, in his spare time, a coder, one of a small group of developers who work undercover in China to design systems to circumvent the largest, most sophisticated system of online censorship anywhere in the world. The government is probably monitoring him, he says, but has yet to take any action.

His experience illustrates how China’s government allows a few cracks in the Great Firewall, but also how the power of this massive system of online censorship lies in the fact that no one knows exactly where the lines are drawn.

Although tens of thousands of websites are blocked, the Chinese government appears to tolerate having a small number of people able to vault the Wall and access the outside world. Yet for those who design systems to help netizens do just that, a knock on the door and a visit by the authorities remains a constant threat.

“I’d be lying if I said I wasn’t concerned about the risks,” the IT professional said in an interview. He spoke on the condition that his real name, his Internet alias and the name of his project be concealed. “But life is a constant adventure. I try to guess where the bottom line is for the government, weigh the risks and steer clear of the line. I won’t stop what I am doing just because it is risky.”

Blocked by China’s censors: Facebook, YouTube, Google, Twitter and Instagram, as well as the websites of many major news organizations. Yet a small minority of people, perhaps a few million in an online population of around 700 million, do get around the controls.

The party’s limited tolerance is, experts say, partly a social safety valve, partly an effort to keep the country’s globally mobile elite happy, but perhaps mainly just recognition that a North Korean-style effort to wall off the Internet entirely would be immensely damaging for business and the economy.

To stay on the right side of that vaguely drawn line, the IT professional has a simple rule: He doesn’t actively promote the tool he has developed to circumvent the Wall, nor does he offer “non-technical” support for users.

“For now, the government is allowing some space for circumvention technology developers, as long as they are not working for political or financial purposes,” he said.

Others, though, have found themselves suddenly on the wrong side of that line. A leading coder who went by the alias ­clowwindy was one of them.

He had been developing a popular system called Shadowsocks that allowed users not only to circumvent the Great Firewall but also to conceal from the authorities that they were doing so.

That is something the Communist Party clearly felt to be a threat.

“Two days ago, the police came to me and wanted me to stop working on this,” clowwindy posted on Github, a website dedicated to hosting open-source software projects, on Aug. 22. “Today, they asked me to delete all the code from Github. I have no choice but to obey.”

Clowwindy ended his last post with an impassioned plea. “I hope one day I’ll live in a country where I have the freedom to write any code I like without fearing.”

Three days later, on Aug. 25, another developer was forced to remove code on Github for GoAgent, another popular free circumvention tool in China.

“Everything that has a beginning also has an end,” its developer, nicknamed phuslu, posted.

Experts said it has become harder to get around the Great Firewall during the past two years, while the list of banned foreign news websites has expanded.

But in this cat-and-mouse game, the cat doesn’t always win.

(Washington Post illustration; iStock)

Clowwindy, who did not respond to an emailed request for comment, became an instant hero to the coding community after his withdrawal: Since then, other developers have preserved and have continued to update the coding on which Shadowsocks is based.

“One clowwindy down! Thousands of clowwindys stand up!” one user posted on Github.

Around the world, many other developers are dedicated to combating online surveillance and censorship — and not just by the Chinese government.

Commercial virtual private network (VPN) suppliers form a fast-growing business and are popular here. They offer a tool that allows users in China to tunnel into the Internet via a different country — circumventing censorship and experiencing the Web as if they were in the United States, for example, albeit at a cost in terms of browsing speed.

But they, too, face a constant battle to stay ahead of the Chinese censors, who clamp down during sensitive political anniversaries or major events like the annual National People’s Congress gathering in Beijing.

“The Chinese firewall is constantly adapting, but not in a predictable or consistent manner,” said David Lang at Express VPN in the British Virgin Islands. “A VPN setting that works for a user in Shanghai may not work for a user in Beijing. A solution that works today may not be working tomorrow.”

Free systems such as Lantern, Psiphon, Ultrasurf, Tor and Streisand secure servers are inspired by the idea that information should be able to flow both freely and confidentially over the Web.

Lantern started out with the idea that users in countries with free Internet access could share their bandwidth with those in censored countries. It saw its service partly blocked in China in late 2013 after it started to gain popularity, but it has since been relaunched and seems to be working well again. Tor’s Nathan Freitas has been inspired by the Tibetan freedom and rights movement; Joshua Lund developed Streisand servers in reaction to Turkey’s censorship of social media and the Internet in 2014.

The State Department and the Broadcasting Board of Governors have helped fund several projects, although some in Congress and in the industry argue that the U.S. government could help tear down China’s Firewall if it spent only a few tens of millions of dollars a year on battle-tested circumvention systems, so that those work-around systems could afford to expand their user bases.

GreatFire.org is another group dedicated specifically to taking down the Firewall, and it offers a free browser on Android that allows users in China to access any website they wish to visit. It uses a technique known as “collateral freedom,” relying on cloud-
hosting services used extensively by Chinese businesses.

There is no way to block the information without blocking the entire cloud service, something that would inflict considerable “collateral” damage on the Chinese economy.

“To be honest,” admitted GreatFire’s Charlie Smith, users “mainly seem to be interested in Facebook and YouTube.”

However, a start page in the app offers Chinese-language news from blocked sites, he adds. “That has proved increasingly popular, and we sent 839,000 visits to blocked news stories between late April and late May alone,” he said.

Smith, who uses a pseudonym to evade detection, says the harder the Chinese clamp down, the more likely it is that the Chinese people will fight back.

Censoring foreign news about corrupt party officials might not come as a surprise, but blocking news about last year’s stock market crash really upset people, he said.

Jeff South, an associate professor at Virginia Commonwealth University who has been spending part of the year teaching in China, says the majority of his students wanted Internet freedom. Yet when they jump the Wall, he says, they use that freedom in ways most young Americans do — “to muse on everyday life or comment on pop culture or watch music videos.”

“The students didn’t use it to seek out prohibited political content about Tiananmen Square, China’s leaders, the Cultural Revolution or other sensitive topics,” he said.

It is an open question whether that’s because they don’t know what to look for, whether they self-censor, or whether they are simply “proud of their country” and don’t want certain beliefs challenged, South said.

These days, the IT professional believes that the Great Firewall is damaging his country — by not allowing information in, as well as by preventing China’s dirty laundry from being aired.

“The youngest generation in China has a limited perspective, because they never get the chance to meet people outside China. People outside China have a lot of misunderstandings about China because they don’t get to interact with people behind the Wall,” he said.

“The Firewall splits the world apart. There are now two worlds in cyberspace: There’s the world, and there’s China.”

Xu Yangjingjing contributed to this report.