Tianya replied to China Daily through an e-mail on Wednesday, admitting that the website was hacked but could not give the figures related to the number of people affected.

"Hackers claimed to have grabbed information about 40 million users, but so far our check shows the actual number is smaller than that," said the e-mail.

The forum said it had reported the case to the police, and the motives, methods and scales of the hacking case were still under investigation.

Apart from Tianya and CSDN, the Sina weibo, the most popular micro-blogging service, was also reported by many of its users as having been hacked on Dec 23, which Sina did not confirm.

China Daily found lots of ads appearing on many verified Sina micro blogs in mid-December, and some of them later claimed to have been hacked. A China Daily reporter's micro blog was abnormally logged in at many different locations, including Henan and Fujian provinces, from Nov 30 to Dec 5, places where he had never been.

The Sina weibo on Wednesday reminded its users to check the logging time and place to judge whether their accounts were being accessed by hackers.

Sina refused to comment on the issue when reached by China Daily on Wednesday.

Dangdang.com, one of China's biggest e-commerce websites, issued a release on Thursday, admitting that some of the company's data was hacked. The company refuted rumors that more than 12 million users' information was leaked, saying that the hacked information in question was six months old, and those hacked users will not suffer a loss.

Alipay, an online payment tool that boasts of more than 550 million registered users, declared on its Sina micro blog on Thursday that all users should rest assured that none of them had been leaked.

No netizens have reported direct economic loss due to the information leakage as of late Thursday.

IT technicians at a power company in Huaibei, Anhui province, discuss Internet security issues on Oct 7. [Provided to China Daily]