US antivirus and firewall vendor Fortinet is investigating claims that its technology has been sold to the government of Myanmar (formerly Burma) in breach of a US embargo.

The investigation began after a report by the OpenNet Initiative, a group set up by Cambridge, Harvard and Toronto universities to monitor web censorship. 

The group claimed that Fortinet's products were being used to block sites for internet users in Myanmar which are deemed unsuitable by the authorities.

In tests the group found that 11 per cent of websites were blocked by the technology, but that this rose to 85 per cent for web-based email sites.

Some 80 per cent of sites containing information critical of the Myanmar government, or with pro-democracy content, were also blocked.

"Burma's commitment to regulating internet content through technical methods is demonstrated by its purchase and ongoing implementation of filtering software from the US company Fortinet," the report states.

"Our research suggests that Burma continues to seek to refine its censorship regime. Burma's system of internet control shows no signs of lessening, and may worsen as it moves to a more sophisticated software product and as the state moves to tighten online restrictions."

A spokesman for Fortinet denied any wrongdoing by the company and promised an investigation. "Fortinet uses a two-tier distribution model and does not sell directly to end users," he said.

"Our channel partner contracts explicitly state that partners must obey all US export laws and prohibit partners from exporting, re-exporting, diverting or transferring Fortinet's products to any destination, entity or person restricted or prohibited by US export controls.

"We are currently investigating the matter relating to Myanmar and evaluating appropriate actions."

The security company does not have a channel partner in Myanmar and is checking to see how the technology came to be installed.

Myanmar was placed under embargo by an executive order of Bill Clinton's in 1997 after its government launched a crackdown on pro-democracy protestors. The EU imposed its own sanctions in 1996.