More than 100 Internet companies in Beijing signed an agreement on Thursday to fight the distribution of illegal and improper information online, promising they will punish those spreading fake messages and accept public supervision.

The companies are required to set up 24-hour hotlines to deal with reports from residents, ensuring that problems can be addressed in a timely manner, according to China's Internet security watchdog.

Under the agreement, if the corporations are alerted to unverified rumors, to information involving terrorism or to the distribution of pornography, they will clean them out and punish the troublemakers, the State Internet Information Office said.

Companies that cannot or will not respond to reports in a timely manner will be exposed, criticized and potentially even closed, an official of the reporting center under the authority said.

The center has received more than 4.66 million reports and exposed more than 200 Web companies suspected of spreading improper information since it was established 10 years ago, said the official, who declined to be named.

"We also reward those who provide valuable reports, hoping to inspire more people to join us to crack down on illegal and improper online information," he said.

The center received 680,000 reports, including 9,000 pieces of information relating to terrorism, over the past eight months, and paid more than 2 million yuan ($326,000) to more than 800 informants, according to an official statement.

"The report service can encourage residents' efforts to purify the cyber environment, while the Internet companies can also make use of the channel to build their credibility and shoulder more social responsibility," he added.

Li Tong, chief inspector of Sina.com, one of the country's largest websites, said his company has published its hotline on the website's front page and dealt with more than 15,000 pieces of information provided by the center.

"We supply a reporting channel for each product of our company, aiming to guarantee that reported clues can be followed up," Li said, adding they have deleted about 5 million pornographic messages on Sina Weibo, Chinese largest Twitter-like service.

Wang Yi, deputy chief editor of Baidu.com, China's largest search engine, said her team will reply to informants within 24 hours, adding that Baidu can track down serious offenses, such as those involving terrorism, within four hours.

Wu Chenguang, chief editor of Sohu.com, another large site, said the biggest challenge is to confirm whether reports are true or false.

"The reports are sent to different divisions in accordance with their contents, and will be deleted if they appear to be illegal," Wu said.

"But if we are not sure whether the reported information is proper or not, we have to ask authorities, such as the public security departments and the nation's Internet information office," he said, adding that this consumes time and labor resources.

To alleviate the problem, Internet giant Tencent has assigned more than 200 employees to manage reports, according to Chen Weisi, a senior manager. The number of reports each day can reach 600,000, Chen said.

[email protected]