Wang Zhihong (31), who works for an American medical equipment company in Beijing, finds the best way to keep up to speed about his company's products is to check out the videos his firm posts on YouTube to inform the global workforce. Sounds straightforward, but it's easier said than done.

“Our Beijing office can’t open it, so HQ has to mail a DVD copy, and it takes quite a while to reach us. Also our Beijing office has difficulties getting access to Gmail, so our company has had to create an internal email system,” says Wang.

Tweeting a football match result, liking a YouTube video on Facebook, posting a photo on Instagram, or sending an email using Gmail – these are the everyday quotidian activities of the global online citizenry.

In China, home to the world's largest online population with 650 million users, an increasingly rigorous internet crackdown means doing any of these tasks is at-best a complicated, and sometimes impossible, challenge.

Since coming to power in late 2012, president Xi Jinping has overseen a campaign to shore up the ruling Communist Party’s grip on power, combatting corruption and making sure the whole country is “on message”, be they online or offline.

People spend a lot of time online in China. In 2014, Chinese “webizens” spent an average of 26.1 hours online per week, just over an hour more than in 2013 and nearly double the time spent online in Ireland.

Internet watchdogs are trying to increase their oversight of those hours spent online in China.

Using its system of controls, known as the Great Firewall of China, the internet in China now functions like a giant intranet, where the online world is tightly regulated, and global services such as Google, Twitter, Facebook and YouTube are blocked, as are many foreign news websites such as the New York Times.

E-commerce sites like Alibaba, which last year listed to great fanfare on the New York Stock Exchange, and the search giant Baidu, have a free hand to operate in the booming China market, as foreign competitors cannot access the market.

Of the 649-million-plus Chinese webizens, the number of people accessing the internet from mobiles totalled 557 million by the end of last year, up 56.72 million year on year and accounting for 85.8 per cent of China’s total online population, according to a report by the China Internet Network Information Centre.

China has always sought to balance the business opportunities offered by the internet with the government's need to muzzle free speech and dissent, particularly anything that challenges the Communist Party of China.

Censors from the Cyberspace Administration of China keep a tight grip on what can be published online.

The administration is run by Lu Wei. As head of the regulator for the world’s biggest online population, he is one of the most powerful people in the world.

He recently visited Facebook, which has been blocked in China since 2009. Ahead of his tour of the Facebook headquarters, Facebook founder Mark Zuckerberg reportedly left a copy of a book of speeches by president Xi Jinping, The Governance of China, lying around on his desk.

While Lu never revealed if it made any impression on him, the CAC head sees his task as clear.

“We should establish an internet order that helps maintain security,” he said in a keynote speech at the Fifth China-UK Internet Roundtable in 2013.

“The internet is a worldwide platform for sharing information. It is ‘a community of common interests’. No country is immune to such global challenges as cybercrime, hacking and invasion of privacy. In cyberspace, it is becoming increasingly difficult to uphold security for one’s own country by sacrificing that of others,” he said.

For the most part, China’s social media companies and web portals censor themselves, fearful of losing their license to operate in China, and it is rare for companies to be chastised in public.

However, this month we got an insight of how the campaign has been stepped up when the popular web portal and social media firm Sina was singled out by the regulator as running the most complained-about major website in the country.

Bosses from the Nasdaq-listed Sina, which also operates China's most popular microblog Sina Weibo, were summoned over "massive numbers of public complaints about its law violations" and warned that the web giant will face suspension of its internet news services if it fails to improve censorship of illegal content.

Since the beginning of the year, the administration has received 6,038 complaints about Sina, more than any other web portal, the Xinhua news agency reported.

According to the reports, “Sina has spread illegal information related to rumours, violence and terrorism, pornography, swindling, advocation of heresies and has distorted news facts, violated morality and engaged in media hype.”

Sina has also published some false news because of too much haste and its censorship of user accounts has been poor, “undermining online order and damaging public interests,” the Cyberspace Administration of China added.

Positive energy

Sina responded by saying the group will intensify censorship and publish more information with “positive energy”.

“Positive energy” is something that the regulator’s chief Lu wants more of on the internet.

“Positive energy is meant to give people confidence and hope, encourage people to love their country, society and life, as well as to pursue nice things. Everything we do is ultimately for the sake of spreading positive energy. Positive energy knows no boundaries. If everyone were to spread positive energy on the internet, the world would be a much better place,” he said.

The vast majority of Chinese people don’t care about the crackdown, as they can use the domestic versions easily.

“For social websites such as Facebook and Instagram, I don’t use them much because we have Sina Weibo or Youku Tudou, which is enough. Most of my friends are here in China,” says Wang.

For foreigners in China, and Chinese webizens with a global focus, a particular irritant has been attacks on VPNs (virtual private networks), the software this correspondent and millions of others use to circumvent the Great Firewall.

In the middle of January this year, the situation became considerably more complicated. VPNs, including some popular brands such as Astrill, stopped working and seemed to be under constant attack. While the shutdown is patchy – iOS services on iPhones would no longer work, but desktop Macs were fine, for example – it was clearly a concerted attack.

As well as being irritating, it’s slightly puzzling. VPNs were largely tolerated until about a year ago, allowing those who needed to access, say, scholarly research online to help with China’s innovation drive, to use VPNs to get into overseas sites. The majority of the population weren’t interested in using sites like Google or Twitter anyway, as the domestic versions, Baidu or WeChat, were fine for their purposes.

Their use was not encouraged – applying for a VPN, you could draw attention to yourself, and authorities would contact people buying overseas VPNs and ask them why they were doing it. But generally those who needed them could get them.

A woman who gave her name as Winnie (32), who works in human resources for an English school, is responsible for hiring foreign teachers. “Without a VPN, I can’t get onto foreign websites or Facebook to look for teachers. So I have to ask friends who are abroad to post the job for me. Also, it is difficult to keep contact with teachers or follow them on Facebook after they go back to their countries.

“As well as this,” she says, “I like watching videos on YouTube. Sometimes, I find myself so isolated from the outside world. Are we heading in the same direction as North Korea?”

Crackdown

The crackdown on VPNs was part of the campaign aimed at the “10 Chaoses”, which included stopping people from using avatars and account handles, or information “that violates China’s constitution or the country’s laws, subverts state power, undermines national security and sovereignty, or is deemed rumour-mongering.”

Internet regulators began insisting on a real-name registration system for online users of instant messaging services, Twitter-like microblogs, online forums and other websites.

According to the regulation, malicious content included “the promotion of cults and the dissemination of pornography or extremism”.

Internet activist groups in recent weeks have pointed to the arrival of a powerful new weapon called the “Great Cannon”, whereby the authorities can launch major “distributed denial of service” (DDoS) attacks to enforce censorship rules.

There were a number of these attacks on the software development platform GitHub last month, taking aim at anticensorship in China projects hosted there. It was the largest attack the site has endured in its history.

The Great Cannon sits between the web server and end users, where it hijacks foreign web traffic to or from individual IP addresses, injects malicious code as a “man in the middle”, then sends it to where it wants, according to greatfire.org, a nonprofit that runs mirror images of sites that are blocked inside China.

Last month, citing independent research from Citizen Lab at the University of Toronto, the Great Cannon intercepted web and advertising traffic intended for Baidu and redirected it to the programmers’ site GitHub, as well as GreatFire.

GreatFire blamed the Cyberspace Administration of China for carrying out the cyberassault. “When we first blogged about this attack we did not want to level accusations without evidence. Based on the technical forensic evidence . . . and the detailed research that has been done on the GitHub attack, we can now confidently conclude that the Cyberspace Administration of China is responsible,” it said in a report on the incident.

Scorn

GreatFire said it had predicted that China would increase their use of “man in the middle” attacks to censor encrypted websites. “We now sadly predict that the DDoS attacks against us and GitHub are likely to signal a ramping up of attacks against foreign internet properties. These kinds of attacks should draw scorn and criticism from government officials of all countries around the world,” GreatFire said.

Not all the methods employed by the government are as high-tech as the Great Cannon.

The government, through various political groups, such as the Communist Youth League, encourages millions of online commentators to post pro-government comments online and go after the government's critics.

They are known as the “5 Mao” brigade, as they are alleged to be paid five mao (about 38 cents) per post.

Of the big media outlets to suffer at the hands of the Great Firewall, the New York Times and the Bloomberg news agency are among the highest profile.

The New York Times ran a story in 2012 about the family wealth of then-premier Wen Jiabao, and its Chinese-language website was quickly blocked; the government has since made it difficult for reporters to get visas for China.

On the tech side, the New York Times is taking steps to ensure people can still get access to its articles.

These include “mirroring”, where several copies of stories from the Chinese-language website appear on other sites online, and the censor has to track them down.

Like so many other forms of online censorship, what you end up with is a form of cat-and-mouse, with a new target popping up every time the censor catches up. Even though it is banned, China is the fourth largest source of online traffic for the New York Times.

The crackdown is having a negative impact on business, with foreign firms particularly incensed.

"These worrying trends illustrate how excessive tightening of internet controls can choke business growth and stifle investment in technology and R&D – areas which are crucial for China's development," says European Chamber of Commerce president Joerg Wuttke. "This is compounded by the fact that these measures are also discouraging much-needed foreign talent from relocating here. Restricted access to key internet tools is not merely an unfortunate inconvenience for individuals – it is an increasingly onerous cost of doing business here that many companies are finding harder to bear."

A survey by the chamber showed 86 per cent of reported a negative effect on their business as a result of certain websites and online tools being blocked.

At the same time, domestic firms are able to take advantage of the situation and local tech firms like Alibaba, Baidu and online social media player Tencent are doing great business.

You also have anomalies, such as Twitter, which has its EMEA headquarters in Dublin, opening an office in Hong Kong to try to woo mainland Chinese advertisers, despite the six-year ban.

Twitter’s Hong Kong office will seek out mainland companies that want to advertise overseas, even though most of China’s webizens will be unable to view the ads.

The main targets will be "big advertisers looking to reach overseas", said Peter Greenberger, Twitter's sales director for emerging markets.

And even though Twitter is banned, state media such as the Xinhua news agency, the Global Times and the China Daily happily promote their Twitter feeds on their websites as they try to gain readership around the world. Some names have been changed to protect the interviewees' identities