Chinese users can no longer access sites such as Facebook
Web browser Opera has closed a loophole which allowed Chinese users to access sites banned by the government.
At the weekend mobile users of the Opera Mini browser were asked to upgrade to a Chinese version.
According to the BBC's Beijing Bureau, this version no longer allows access to sites such as Facebook.
Previously traffic ran over Opera servers bypassing the so-called Great Firewall of China, making the browser popular with Chinese users.
Opera confirmed that it had started directing users of the international version of the mobile browser to the Chinese version on 20 November.
"The difference between the Chinese and the international version is that the former connects to compression servers within China.....benefits are higher speed, lower costs and an overall improved mobile web browsing experience," the firm said in a statement.
It was not prepared to discuss the "background for this decision".
But there was plenty of speculation on the blogosphere.
"Let me guess what has happened here. The Chinese government has put pressure on Opera to close down that free access. And like most companies, they complied," wrote blogger Carsten Ullrich.