One of China's largest social networking websites could not be accessed for undisclosed reasons on Tuesday.

51.com, a community portal, similar to Facebook, went offline around 4:00 PM, sparking rumors that the site is the latest victim of government efforts to clamp down on objectionable content on the Internet.

The website, with more than 100 million users, has received backing from major venture capital investment firms, including Sequoia Capital China and Redpoint Ventures, also an investor in MySpace.com.

Two other websites also went offline late yesterday, including IT168.com, an information technology forum with 10 million members, and BlogBus.com, a blog site with 5 million users.

The three portals were closed by Xinnet Digital Information Technology, the domain registrar for the sites, according to reports on major Chinese IT portals, including Sina.com.

IT168.com was closed "based on the order from a higher competent department because the website had vulgar information", a report on ccw.com.cn, a major IT news portal, said. The website was back online around 9 pm yesterday.

Dou Yi, CEO of BlogBus, told Neteast.com his website was closed because of an article with "illegal" content posted a while ago.

Xinnet has not said when the other two websites will be unblocked or why it stopped servicing them, the Sina.com report said.

Hundreds of thousands of websites in China have already been shut, insiders estimated, following accusations that they were hosting other websites that provide "harmful information".

(China Daily January 6, 2010)