The problem arose because exhibitors, including major IT companies, were failing to follow security advice issued by the NEC, said communications infrastructure manager Michael George.
"The level of protection of some of the PCs - in fact most of the PCs - was quite shocking. The problems involved globally known organisations, including IT organisations," he said.
A spate of virus and worm infections last year forced the NEC to introduce a policy of disabling exhibitors' internet connections until they had been inspected for anti-virus protection by the NEC's IT staff.
This meant extra overheads, including having to draft in six staff to perform the checks. "By late summer it was clear that there was a problem that needed addressing," said George.
After an evaluation, the NEC invested in two Fortigate-800 firewalls, supplied by Fortinet, which use hardware anti-virus technology to detect viruses on the network in real time.
Traditional firewall products were unsuitable because they would block the non-standard configurations used by many of the exhibitors on their displays, said George.
The firewalls also allow the NEC to manage and configure internet connections for exhibitors, who are allocated temporary IP addresses giving them direct connections to the internet.
The NEC, which claims to have eliminated virus infections on its exhibitor Lan since the firewalls went live towards the end of 2004, plans to upgrade its network to make use of the intrusion detection and prevention capabilities of the firewalls.