Security vendor, Fortinet, has been ordered to suspend sales in America after the US International Trade Commission made a final ruling against it in its year-old patent infringement dispute with Trend Micro.

The disputed patent relates to elements of the antivirus engine used by Fortinet in its FortiGate security appliances, a feature the company will now have to cease shipping to comply with the decision.

Sales of Fortinet's products outside the US - said by the company to account for 70 per cent of its business - will not be affected by the ruling. Current customers and reseller inventory will also not be affected.

The FortiGate series of gateway appliances also provides firewall, VPN, intrusion detection/prevention web filtering, antispam, traffic shaping, so the potential hiatus in anti-virus for new customers is likely to be inconvenient rather than critical.

The company said it planned to comply with the patent within the next 60-90 days, updating current systems with new software. This could mean licensing technology held by Trend or simply rewriting the software in an unspecified way to avoid the problem.

"Fortinet firmly believes we do not infringe on Trend Micro's antivirus patent," founder, president and CEO, Ken Xie, said. "We are committed to ensuring that our US business operates as usual with no impact to customers and partners, and we are confident that our forthcoming antivirus software enhancements will avoid Trend's patent," he said in a web statement.

Many appliance vendors use anti-virus engines from Trend, Symantec or McAfee (the latter two licensing elements from Trend). Fortinet was unusual in going its own way. Given reseller inventories, Fortinet will probably be able to continue to sell to new customers until those supplies are exhausted, by which time it will aim to have fixed the issue for new products.

In May, the US international Trade Commission made an initial ruling against Fortinet in the case, but the latest judgment is final confirmation of that decision.