Paid virtual private networks (VPNs) are quietly catching on in China as a way to access forbidden websites, analysts say, while authorities are leaving them alone until they become more popular.

VPNs designed for secure Internet use in offices have spread over the past half year among expatriates and tech-savvy Chinese since the popular social networking website Facebook was blocked. Twitter and YouTube are also blocked in China, which uses a filtering “firewall” to block Internet users from overseas website content that challenges the Communist Party. The rise of VPNs comes as China defends its curbs on the Internet after the world's biggest search engine provider, Google Inc., threatened to shut down its Chinese site over censorship and a severe hacking attack. “So long as the VPN is outside of mainland China, it should not be a problem,” said Danny Levinson, publisher of “We use our own VPN and it works fine.” Chinese authorities seldom block foreign-based paid VPNs and are likely to leave them be as long as the number of users stays small, a veteran IT analyst in Beijing said. “It's a little steam valve,” the analyst said. “But if China's army of netizens gets in on these things, there you are.” The government aggressively shuts down free proxy servers, which can also unblock forbidden sites and are more widespread. Paid foreign VPNs have been blocked just once, ahead of National Day in October last year, users say.

About 10 foreign VPN services are popular in China, but there are no estimates on the number of users, China IT analysts say. VPNs work as overlays on top of larger computer networks, using encryption to make private traffic safe in the less secure environment of the Internet. “In China, accessing Facebook and Twitter are the main reasons why clients sign up,” said Chris Matthews, who runs the California-based Freedur and targets expatriates. “The Chinese government doesn't care about us, they just don't want their citizens stumbling upon something on the Internet that will cause them to (raise) questions.” But technical and cost obstacles could stall growth in China's VPN use outside offices, analysts say. Some VPNs bring Internet browsers to a crawl or require users to make tough changes to their computer systems before working at all, they say, while Chinese nationals without foreign currency credit cards often have no way to pay for them.