Computer users should not relax their guard just yet, with terrorist groups still suspected to be plotting cyber attacks a year after September 11.

Terrorism Research Centre director Mathew Devost warned complacent network operators who thought terrorist groups had abandoned attempts to hack critical infrastructure were leaving the door open to attack.

"It hasn't happened yet, but that doesn't mean there isn't a risk," he said. "It just means the variables haven't aligned to ensure a successful operation."

Mr Devost - whose company consults to a number of US corporate and government clients on physical and virtual counter-terrorist strategies - told a briefing at the US Consulate General in Sydney today that the September 11 attacks had made cyber terrorism more attractive to some groups.

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