New software will be released at the end of the month that could cripple the great firewall of China and allow citizens of repressive regimes to bypass web censors.

The software, known as Psiphon (PDF download), has been developed by the Citizen Lab at the University of Toronto, a group of programmers and political scientists designing new ways for the internet to affect social systems.

Psiphon will allow computer users in repressive regimes to use volunteer PCs as proxies without the risk of being identified.

"I was always interested in the idea of using computers for social and political change," Nart Villeneuve, who has been dabbling with the project for about two years, told the Toronto Globe and Mail.

"It was a matter of creating a program for really non-technical people that was easy and effective."

Volunteers can allow their machines to be used by overseas users to bypass security filters. The PC's owner has to assign a user name and password to the 'dissident' user and, once completed, the PC can be used remotely to access information.

The system will be harder for censors to block since it relies on building trusted relationships rather than by publicising proxy addresses.

The creators see the code being used in conjunction with activist groups to enable 'forbidden' information to be accessed and spread.

One crucial advantage is that the remote user has no software to install on a PC, which could leave tell-tale clues for investigating censors.

The application's traffic would also be difficult to block since it uses port 443, which is predominantly used for financial data and is seldom blocked.

"Unless a country wanted to cut off all connections for any financial transactions they wouldn't be able to cut off these transmissions," Professor Ronald Deibert, the director of Citizen Lab, told the paper.

The final code, which is written in Python, supports multiple platforms.