BEIJING - Four people have been detained by police and eight others punished after they were found guilty of fabricating a massive leak of online personal data by hackers over the past month in China, the country's Internet watchdog announced Tuesday.

China's leading anti-virus software provider, Beijing-based Qihoo 360, claimed in late December that the personal information of more than 6 million users of the China Software Developer Network (CSDN), the country's largest programmers' website, had been leaked by hackers. That raised concerns about web security and triggered widespread panic.

The company said the leak included user IDs, passwords and e-mail addresses in clear text. The hacking case later escalated after the personal details of subscribers to more websites, including popular online shopping, gaming, social networking and even financial institution sites, were said to have been leaked.

However, a police investigation into the cases has found that most of those websites had not been attacked by hackers at all over the past month, or that they had been attacked without their subscribers' information being leaked, a spokesman with the National Internet Information Office said Tuesday. The leaks were merely a fabrication.

Police have cracked 12 such cases, nine of which involved insiders working for the companies stealing and illegally selling online personal data, and three of which involved a fabricated information leak, he said.

Four people have been detained and eight others received formal admonishments in punishment according to the country's public security regulations, he said.

In the CSDN case, a 19-year-old jobless man surnamed Xu was found to have faked a large-scale leak of personal data just to "show-off," and he had received "admonishment" from the police, the spokesman said.

As for the leak of some users' passwords on a few well-known social networking websites, such as Sina Weibo and www.kaixin001.com, police found that hackers decoded the passwords through guesswork and the personal data banks of the websites had not actually been attacked, he said. Police have confirmed the identities of the hackers and are hunting them, he said.

China has the world's largest online population, with the number of Internet users reaching 485 million by the end of June last year, according to the China Internet Networks Information Center (CNNIC).

In the first half of 2011, 217 million Chinese Internet users, or 44.7 percent of the country's total online population, were attacked by malware, including viruses or Trojan horses, and 121 million had the experience of having their accounts or passwords stolen, CNNIC data shows.

Last month, authorities in Beijing, Guangzhou and Shenzhen launched an Internet supervision measure requiring local microblog operators to implement real-name registration requirements for users, a move designed to curb online rumors and enhance social credibility.

"It can be seen from the recent cases of personal data leaks that they fabricated such information for different purposes, such as for showing off, defrauding others of money, promoting their web security products or disturbing and disparaging the real-name registration move," the spokesman with the National Internet Information Office said.

"The National Internet Information Office, the Ministry of Industry and Information and the Ministry of Public Security will severely punish those who attack websites and leak personal information or fabricate and spread rumors in this regard," he said.

"We will continue to take effective measures to protect the security of online personal information. The website operators should enhance their anti-virus and anti-hacker capabilities and guarantee the information security of their subscribers," he added.