Chinese search giant Baidu has fired four employees after it emerged that they may have accepted bribes to delete posts from its website.

Three of the former employees have also been arrested for accepting cash to delete forum posts. Baidu's spokeswoman Betty Tian told BBC News that the sums involved amounted to “tens of thousands of yuan” (thousands of pounds).

“Baidu has always firmly cracked down on the illegal behaviour of online posts deletion for payment,” said Tian, adding that illegal deletion of online posts is a major problem in China.

Chinese media reports suggest that it is fairly common for individuals or companies to pay money to have controversial or negative posts deleted from websites and blogs.

Tian said that Baidu would proactively report illegal activity to the authorities.

It is notoriously difficult for web companies to operate in China, due to the country's strict internet regulations. Often descibed as “The Great Firewall”, the system bans content and websites that are deemed to be politically sensitive or anti-government.

In November 2011, China's top IT firms including Baidu, Tencent and Alibaba pledged to step up the regulation of their services, as government authorities intensified calls to control the development of the nation's internet.

Representatives from 39 companies made the pledge during a government-sponsored meeting, stating that “internet companies must strengthen their self-management, self-restraint, and strict self-discipline,” according to a report from state-run press agency Xinhua.

The head of China's IT authority, the State Internet Information Office, said the companies must take the lead in enhancing the credibility of online media companies while also strengthening their management.