A document released by a hacker on the Internet revealed personal information of up to 6 million account. [Web photo]

A document released by a hacker on the Internet revealed personal information of up to 6 million account holders at China's largest online community for computer programmers, Chinese Software Developer Network (CSDN).

CSDN posted a letter of apology on its website, saying that the account information leaked came from a database built prior to September 2010, and the cause of the leak is still under investigation.

The computer programmer community site may have been just one of the websites exposed to the security leak. Internet companies including Renren and Kaixin reportedly also had their users' private information stolen, but the companies denied the claims.

A slew of Internet privacy blunders have taken place during recent years. In early November, a large number of Microsoft instant messaging and e-mail users had their accounts stolen. This month, some Sina Weibo users voiced suspicion that their accounts were stolen after being forced to change passwords before logging onto the microblogging website.

China's business press carried the story above on Friday.