Three employees from Baidu, China's largest search engine, have been arrested for being paid to delete online posts on its website, the company confirmed Sunday.

The three were suspected of colluding with external partners to delete online messages. Another employee was also fired for attempting to delete posts for cash, but not arrested. 

"Baidu has fired the four. If we discover such cases, we will severely punish staff. Baidu will close the loopholes by strengthening management to maintain order in our communication platform," Li Guoxun, a Baidu public relations officer told the Global Times Sunday.

There has been one similar case previously, said Li, but police became involved this time due to the large amount of money involved.

The money would run into tens of thousands of yuan, said a Baidu source Sunday, on condition of anonymity.

According to internal communications from Baidu, an employee, surnamed Lu, was working with professional agents to delete posts. Lu was arrested on July 16 under suspicion of bribing non-government staff, the Beijing News reported.

Another two suspects, surnamed Sun and Xu, were detained on July 20 and 23. A non-Baidu employee was also detained, the report said.

As a way to remove negative reviews, the post-deleting industry has become popular, with more than a million results in Baidu's search engine under the keywords "professional post-deleting."

A member of staff from a post-deleting company named Beijing Haotian Lianmeng, said that it costs 1,000 yuan ($159) to delete an article from forums, 2,000 yuan to remove one from a blog and 3,000 yuan to delete a piece of news posted on a news portal, like Sina.

"We can offer a professional long-term maintenance service for a company, 150,000 yuan to 200,000 yuan a year. If you choose this service, we will keep an eye on your company around the clock and delete any negative messages," said the staff member, surnamed Liu.

Liu also claimed that he knew insiders in Internet companies, who could help him.

Wang Sixin, a professor of media law from the Communication University of China, said companies have the right to delete comments if they are false or slanderous, but this must be done legally. 

"Those illegal acts in deleting information at will might hinder public communication online and then affect consumers' decisions to some extent, so legislation on this issue is urgently needed," Wang said.