China already has some of the world’s most far-reaching online restrictions. Last year, the government blocked more than a million Web sites, many of them pornographic, but also Facebook, Twitter, YouTube and Evite. Recent regulations make it difficult for individuals unaffiliated with a company to create personal Web sites.

When it comes to search engines and microblogging, dictates from the central Propaganda Department filter out topics and words that the Communist Party deems a threat to national stability or its reputation. At public cybercafes, where much of China’s working class gains access to the Internet, customers must hand over state-issued identification before getting on a computer.

The new measures, it would appear, are designed to eliminate a loophole in “Internet management” as it is called, one that has allowed laptop- and iPad-owning college students and expatriates, as well as the hip and the underemployed, to while away their days at cafes and lounges surfing the Web in relative anonymity. It is this demographic that has been at the forefront of the microblogging juggernaut, one that has revolutionized how Chinese exchange information in ways that occasionally frighten officials.

“To be honest, I can get Internet at home or at work, but it’s nice to just sit in a comfortable place and surf the Web,” said Wang Fang, 28, an advertising sales agent who often conducts work from the leather wing chairs at Kubrick, a high-ceilinged, smartly designed cafe that unplugged its router earlier this month rather than pay for the software. “If there’s no Internet, there’s no reason to come here.” The manager said the loss of Wi-Fi had already led to a 30 percent drop in business.

The Dongcheng Public Security Bureau did not respond to requests for comment on Monday, but according to its publicly issued circular, the measure is designed to thwart criminals who use the Internet to “conduct blackmail, traffic goods, gamble, propagate damaging information and spread computer viruses.” Such nefarious activity, the notice says, “not only hurts the interests of the country and the masses, but has also caused some businesses to suffer economic losses.”