You are driving your car when suddenly you discover you are no longer in control. Somebody has hacked into your vehicle's on-board computer and taken over.
If this sounds like a Hollywood plot or a Top Gear stunt, you are wrong. It can actually be done and Sydney hacker Jonathan Brossard knows how to do it.
The threat from hackers has been in the news recently, with eBay telling 145 million subscribers to change their passwords after a cyber attack and reports of Apple devices being hijacked last week.
Mr Brossard is a ''white hat'' hacker, one of the public defenders whose job is to preserve the integrity of information systems from the attention of the ''black hats''.
The security research engineer does not know of a car that has been hacked on the road but says his company does it for vehicle manufacturers in Europe.
The only way to verify that a car is not subject to cyber attack is to try to break it, fix it and try to break it again, he said.
''The vehicle is remote from me. I am sitting at the desk and I am using the computer and driving your car from another country. I am saying it is possible.
''A car is, technically speaking, very much like a cell phone and that makes it vulnerable to attack from the internet,'' he said. ''An attack is not unlikely.''
Mr Brossard acted as consultant for a video game called Watch Dogs, which was released last week and is set in Chicago. The game explores the impact of technology where everything is controlled by one computer and railways, traffic lights and energy systems are all vulnerable to the hacker.
He believes the game could stimulate interest in a world in which there is a need for more ''white hats''.
''We have come to the point where there is a massive shortage of such people,'' Mr Brossard said. ''Australia is no exception and every country in the world is pretty much in the same situation.
''We are definitely not winning the battle. Hacktackers have become better and better while defensive systems have not significantly changed.''
The murky world of hacking gets a public airing each year at the Black Hat computer security conference in Las Vegas.
At this year's conference in August he says attention will turn to an open back door allowing someone to take control of your computer remotely. He says it already infects 2 million computers worldwide, including Australian machines made by mainstream manufacturers.