In a last-minute climbdown, the Chinese government announced today that it will delay the launch of censorship software that was supposed to have been sold in every computer from tomorrow.

The postponement comes after an unprecedented wave of online opposition, protests by foreign governments and calls by prominent bloggers for Chinese netizens to climb, attack and demonstrate against the "great firewall".

Xinhua, the state news agency, reported the change of plan four hours before the software launch was due.

"China will delay the mandatory installation of the 'Green Dam-Youth Escort' filtering software on new computers," it said in a terse statement attributed to the ministry of industry and information technology.

The authorities looked likely to miss their deadline for the rollout of the software that blocks pornographic, violent and politically sensitive content.

The Guardian struggled to find a single retailer who had Green Dam either installed or bundled with computers.

Adding to the mystery, Lenovo, Sony, Dell and Hewlett Packard refused to comment on whether their PCs are now being shipped with the software, as the government ordered them to do last month.

The government says the software is necessary to clear the Chinese web of "harmful content". But critics say it is a misguided attempt to put the internet genie back in the bottle by a Communist party that now has to answer to about 300 million web users.

"Green Dam is a mini-great firewall placed inside every personal computer," said Michael Anti, an influential blogger. "The real logic behind it is that China is a big kindergarten in which even adults are treated as children that need to be 'protected'."

Isaac Mao, a prominent internet commentator, believes the government has made a big mistake: "I think this is the tipping point between the people rising up and those in power trying to suppress them. The great firewall is overloaded and that is why the authorities are trying to move the focus of control to the desktop. But it has annoyed a lot of people. Not just liberals who want free speech but the young who see it as an intrusion into their personal lives."

Although the plan has at least temporarily failed, it succeeded in mobilising people against the censors. Wen Yuchao, a journalist and blogger who goes by the online name North Wind, said more than 1,000 netizens have signed up to his campaign to "climb" the firewall by signing up to proxy servers that bypass the government's controls. He said 15,000 people are joining TOR ‑ one of the most popular proxies ‑ every day, about double the normal rate. Freegate, a proxy that was developed by Falun Gong, has also reported a sharp rise in demand.

Ai Weiwei, a prominent artist and freedom of expression champion, called for an internet boycott tomorrow.

"Thousands of netizens have said they will join the boycott. People are starting to realise how important it is to tell the government what they want," said Ai. "There is nothing the authorities can do [to stop us]. That is what is great about this. It is personal but widespread."

A group of bandit hackers, known as Anonymous, declared "war" on Green Dam and threatened to attack it tomorrow.

According to a source close to the group, they plan to create a remote computer 'bot' that pummels Baidu, Kaixin and other mainland websites with data requests containing forbidden or sensitive terms, such as expletives, Falun Gong, Dalai Lama and "Fifty-cent party member" (the derogatory name given to people paid to post pro-government comments online). They hope the volume of dirty traffic will clog up the keyword filters.

It remains to be seen whether the government will go ahead with Green Dam or a watered-down version of it. But bloggers and free speech advocates say the long-term trend is positive.

"More and more people have accepted 'internet-era values' such as freedom of speech, access to information and participatory democracy," said Michael Anti. "These liberalised people or 'netizens' are changing the social institutions, step by step. In 10 years, more people will be [on the net] which will increase the chance of China having genuine democracy."