Public servants will practise just that when putting their hacking skills to the test in cyber war games this September.

Cyber security experts entering the fray will represent some of Australia's largest and highest-profile government departments: Human Services, Immigration, Defence, the AFP and the Australian Taxation Office.

The war games, devised by the DHS, are designed to push the technical prowess and critical thinking of APS staff as hacking attacks grow more disruptive.

DHS national cyber security manager Narelle Devine said the games, at the department's Tuggeranong offices, will resemble a game of chess in the cyber world.

"We really think that learning to hack is just a way to learn how to defend better," she said.

"They may actually find vulnerabilities on the way we haven't thought about.

"It's stretching that creative thinking. That's what we're trying to foster, thinking like the adversary and thinking outside the box, not just take the steps you're given."

Each department will have a virtual patch to protect from the attacks of their public sector rivals.

Between them will be a cyber no-man's land which they'll hack through to enter their rivals' territory.

When one infiltrates and disrupts their opponent's system, it's game over.

A Lego display wired with electronics and hooked up to the system will bring the cyber attack to life when hackers make its model trains go backwards, turn the lights on and off in enemy territory or find another way to announce their break-in.

The war games will be the first training exercise of its kind between government agencies, but have been adopted overseas.

Ms Devine said the DHS hoped the games would attract more tech-minded staff to the department.

"It's quite attractive for that target audience, that younger generation we're trying to get to," she said.

"We want to be an employer of choice in this space."

The fragility of cyber defences worldwide was laid bare when ransomware created havoc at British hospitals and hit businesses across the globe last week.

Ms Devine said the DHS wasn't complacent about its cyber security.

"The adversary will always be trying something new, so you can't sit back," she said.

There was no sign of overconfidence when asked about her team's chances against its competitors.

"I'd like to think we'd win, otherwise we wouldn't put it on, but I'm not putting money on it."

The event could become an annual competition between departments and businesses may be invited to join next year.