BEIJING, Feb. 7 (Xinhua) -- Last month, a microblogger known as "Hacker Kevin" received a message from a social media follower, accusing a man in northern China surnamed Li of being a child molestor.

Kevin quickly dug into Li's social media accounts and discovered photos of him kissing young boys, chat records showing how he groomed children, as well as him boasting about his behavior.

After blurring the faces of the victims to protect their privacy, Kevin posted the evidence on Weibo, China's equivalent of Twitter, and alerted the local police. Three days later, Li was arrested.

Kevin, who has 780,000 followers on Weibo, has been using social media to hunt and expose pedophiles for more than a year. He is among a group of online vigilantes waging war against online child pornography and pedophiles.

"You may call me a busybody but I have made stopping child porn my mission, and I will stick with it until the end," Kevin says.

An investigation by Xinhua reporters uncovered a large network in China's cyberspace making huge profits by selling child pornography on various platforms, from members-only forums and private social media groups, to live streaming websites and gaming communities.

In one private social media group, those who paid 50 yuan (7.5 U.S. dollars) could become members and access pictures and videos of pornography. The group had nearly 2,000 members by the time it was exposed.

Those who paid 333 yuan a month could become VIP members, and they could not only watch child sex acts live, but also negotiate transactions with agents to engage in sex acts with children. The agents all used pictures of children as their profile photos.

Chat records obtained by Xinhua between a potential customer and an agent showed a sexual act with a young boy cost 2,000 yuan.

In recent years, Chinese authorities have intensified efforts to crack down on illegal online activity against children.

The National Office Against Pornographic and Illegal Publications said that Internet enterprises and individuals who had produced or distributed child pornography were severely punished in 2017.

Last month, the office exposed details of five typical cases uncovered during the crackdown on online pornography.

In one case, police in Zhengzhou City, central China's Henan Province, arrested Wu Pengsheng and three associates for distributing photos and videos of child pornography on a profit-making website.

The case was first revealed last August by an online crusader known as "Xiao Dang." Tipped off by a follower, Xiao registered on Wu's website and collected a large amount of evidence showing him profiting from child pornography. Xiao was also able to uncover personal information about Wu through his email address and alias.

Xiao then posted his findings on Weibo, which soon generated over 10,000 forwards and nearly as many comments, causing huge public uproar. Local police immediately arrested Wu.

A police investigation found that from 2011 to August 2017, Wu and his associates lured more than 100 juveniles to film indecent videos under the guise of "child education."

They then distributed the videos online and raked in over 500,000 yuan. They have been transferred to prosecution authorities.

For those crusading against child pornography, like Kevin and Xiao, these high-profile cases only account for a small part of their work. More often than not, their reports end up leading nowhere.

Kevin says that though local police are quite diligent in pursuing such cases, the anonymity of the Internet makes busting online rings and securing evidence difficult.

"Online suspects are experts in using guerrilla warfare to dodge cyberpolice. It is very difficult to make coordinated arrests when the illegal activities are committed across regions or borders," Kevin says.

"Child porn suspects are very good at exploiting loopholes or grey areas in law to avoid punishment," said Zhang Hongwei, a professor with Jinan University who specializes in juvenile and family law.

As the law stipulates that criminal punishment only applies to those who "publicly" distribute obscene materials, suspects often choose members-only websites and private social media groups to sell child porn, which makes the number of recipients hard to determine, according to Zhang.

To better protect the underage in the digital age, Chinese authorities have taken tougher measures against pedophiles.

In November last year, the government in Huaiyin District, Huai'an City in east China's Jiangsu Province, issued a policy in which all convicted child sex offenders would have their personal information made public, including names, ID card number, photo, age, gender and the nature of their crimes.

The information will be available to the public on law enforcement authority websites and social networking platforms.

The city of Cixi in Zhejiang Province and Shanghai's Minhang District issued similar policies in June 2016 and July 2017, respectively.

Kevin is hopeful that these measures will help deter crimes against children.

"At the end of the day, all the perpetrators will receive the punishment they deserve," he says. "Justice will be served for all the young victims."