There have been spying controversies galore coming out of China with big tech names including Google implicated.

But now it appears the Chinese authorities may have been monitoring and even censoring messages sent through Skype, and with the full knowledge of the VoIP service provider.

A Canadian research group called Citizen Lab is claiming to have found a database, which contains thousands of politically sensitive words which had been blocked by China.

This database is also said to contain personal data on Skype subscribers in China.

The Citizen Lab researchers, who are based at the University of Toronto, claim that this data was picked up by a surveillance system, which had designed specifically to pick up and store messages sent through Skype.

The database, they say, held more than 150,000 messages which included words such as "democracy" and "Tibet".

"These text messages, along with millions of records containing personal information, are stored on insecure publicly accessible web servers", said Citizen Lab's report, entitled "Breaching Trust".

And the team was even able to see all of the details of the people who had received or sent the messages just by using username.

Citizen Lab said it was "clear" that Tom-Skype, which is a joint venture involving eBay and Chinese company TOM-Online, was "engaging in extensive surveillance with seemingly little regard for the security and privacy of Skype users".

Skype president Josh Silverman has responded saying that China's monitoring policies are "common knowledge" and Tom Online is just meeting "local laws and regulations".

"These regulations include the requirement to monitor and block instant messages containing certain words deemed offensive by the Chinese authorities", he said.

He did add, however, that it was not the policy of the group to store messages and he would investigate the existence of the database.