Starting earlier this year, Web police units directed the companies, which included joint ventures involving U.S. corporations, to buy and install hardware to log the traffic of hundreds or thousands of computers, block selected websites, and connect with local police servers, according to industry executives and official directives obtained by The New York Times. Companies faced the threat of fines and suspended Internet service if they did not comply by prescribed deadlines.
The initiative was one in a range of shadowy tactics authorities deployed in the months leading up to the 18th Party Congress, which is scheduled to end Wednesday, in an escalating campaign against information deemed threatening to party rule. The effort, while spottily executed, was alarming enough to spur one foreign industry association to lodge a complaint with the government. Several foreign companies quietly resisted the orders, which posed risks to communications and trade secrets that they take pains to secure.
The events surrounding the party congress magnify the constant challenge facing China's Internet security apparatus, which is to maintain the party's lock on political power without choking off a wired China from the global economy. The more intrusive recent measures appear aimed at plugging some of the gaps in the "great firewall," China's nexus of surveillance and censorship.
"It goes this way pretty much every time there's some big political event in Beijing: The DVDs are gone, the prostitutes are gone and the Internet's slower," said David van Meerendonk, an American who operates an information technology company here. "They're trying to find a balancing point."
Over the past couple of weeks, partial blocking has crippled access to Google and other sites, at times almost completely. It has also disrupted programs that many people here use to circumvent surveillance and reach blocked overseas sites by other means. Some Internet providers have cut service for hours, citing "maintenance." Democracy activists and foreign journalists have reported increased attacks on their email accounts.
On domestic social networks, already vigorously policed, censors have fine-tuned their craft. Sina Weibo, the nation's most popular microblogging site, has experimented with "semi-censorship," as one blog termed it, filtering search results for once-unsearchable terms. One semi-censored term was the Chinese shorthand for the party congress itself: shiba da. Blocking it had prompted some of China's more playful microbloggers to resort to a similar sounding English substitute: "Sparta."
Hu Jintao, China's departing leader, in his report on the opening day of the congress last Thursday, gave no sign of any relaxation in controls.
"We should strengthen social management of the Internet and promote standardized and orderly network operation," he said.
Police and other agencies rely on legions of local censors, automated filtering and strict regulation of Internet service providers. GreatFire.org, a Chinese-based blog that tracks government filtering, found in tests this month that Google email was being partly blocked, and that blocking intensified after the congress began. One possible explanation for the strategy was that "authorities are nervous of fully blocking Gmail," it said. "The government may be scared of a backlash from the urban, educated and young people who tend to use Gmail, not to mention the businesses that rely on it."
In late summer, the police stepped up jamming on circumvention software, according to two party insiders with Chinese security ties. Students who use Freegate, free software backed by the banned spiritual movement Falun Gong, said that as early as August they experienced unusually frequent disruptions.
China says its online security policies are needed to fight pervasive fraud, cyberattacks, pornography and rumour mongering.
But many of the controls seem aimed more at checking anti-government activity. And the latest effort to enlist business represents a new front for the systems, already installed at many hotels, schools and coffee chains. Many corporations, especially foreign companies, use encryption and circumvention technologies to safeguard communications, allowing local employees to use blocked websites and skirt police surveillance.
This past summer, the Internet police in the provinces of Hebei and Shandong ordered three U.S. companies to install the monitoring systems at local joint ventures, according to a spokesman for the Quality Brands Protection Committee, a foreign industry group representing more than 200 major corporations operating in China.
Elsewhere, U.S., Japanese and Korean companies received similar orders, executives said. They requested anonymity because they were not authorized to speak for their companies and feared compromising local business relationships.
The orders, first reported by CNN, cited existing regulations and designated vendors. The police in the Hebei city of Qinhuangdao notified one company that it would face a fine of 15,000 renminbi, or about $2,400, and lose Internet service for half a year if it did not install the system by mid-August.
Technology specialists warned that foreign companies installing the devices could be directly exposed to intellectual property theft and cyberattacks.
"This box, in addition to being able to monitor any queries about Tiananmen Square or Tibet or the Dalai Lama, also would be able to intercept all network communications from the China operations back to headquarters," said Thomas Parenty, an information security consultant in Hong Kong who advises foreign multinationals in China.
The Quality Bands Protection Committee said the organization believed the initiative amounted to overzealous local enforcement rather than national policy. The group raised concerns about the measure with the police and commerce ministries.
The ministries did not respond to questions.
Sometimes, enforcement seemed superficial.
"I said, 'We don't have a network, so I could not use the piece of equipment,"' said the manager of one Western company, recalling the commotion in his office building the day the Beijing police tried to carry out the directive.
"He said, 'Just sign.' So I did," the manager added. "I did not buy any equipment. I think the idea was to create fear that they can and will check."
(Adam Century contributed reporting.)