Symantec's Norton AntiVirus product has blacklisted a piece of software which enables users in China to access websites which are blocked by order of the government.
According to a report in the Financial Times, the firm has said the program, called Freegate, should be considered a Trojan horse.
The result is that users of Symantec's antivirus product in China will be unable to download the Freegate program and use it to access banned sites. Freegate is explicitly designed to bypass controls and there is no suggestion that it contains any malicious or hidden functions normally necessary to qualify a program as a Trojan.
The move raises the question of whether antivirus technology should be used to support government censorship.
A spokeswoman from Symantec UK said it would be "inappropriate" to comment on the matter.
There are more than 68 million web surfers in China. The Freegate program, which supposedly has 200,000 users, gives access to the banned websites by regularly changing proxy server IP addresses.
Security is a growing issue for China's online population. According to research from Chinese Ministry of Public Security, 87.9 per cent of computers in the country were infected with a virus this year. The report said that the worst viruses were the Sasser and Netsky worms.
The government surveyed more than 7,000 departments and 8,400 users.
Dan Ilett of ZDNet UK reports from London.