Citizen Lab, a Canadian research group, said that China has been monitoring and censoring Skype messages, BBC News reported today.

Citizen Lab found a publicly accessible database containing personal information of subscribers as well as thousands of politically sensitive words which had been blocked by China, the report said.

The researchers, who are based in the University of Toronto, said they discovered “a huge surveillance system” which monitored and stored messages sent through the internet instant messaging and telephony program.

The database held more than 150,000 messages which included words such as “democracy,” “Tibet,” and words relating to the Falun Gong, a movement that is banned in China.

The discovery was included in Citizen's Lab report called “Breaching Trust” released last Wednesday. The text messages and the millions of records containing personal information are stored on insecure publicly accessible web servers, the report said.

Computer World said that while the data was encrypted, the encryption key needed to read the data was publicly accessible.

Citizen Lab said that by using one username, it was possible to identify all the people who had sent messages to or received them from the original user.

BBC said that in China, Skype operates as Tom-Skype, a joint venture involving the American auction site eBay and Chinese company Tom Online.

Skype president Josh Silverman said in a blogpost to the eBay subsidiary corporate blog on Thursday that China's monitoring was “common knowledge” but that Tom Online had “established procedures to meet local laws and regulations.”

“These regulations include the requirement to monitor and block instant messages containing certain words deemed offensive by the Chinese authorities,” BBC quoted him as saying.

Silverman said that Tom's policy had been to block certain messages and them delete them and he would investigate why the company had changed its policy.