It's much easier to know what a digital Pearl Harbour won't be. Taking down the Internet or ATM networks, compromising the Social Security database, even hacking into the electric grid - Schmidt and others argue that while each event may be part of a digital Pearl Harbour, none qualifies in and of itself. None would galvanise society, spurring it to action.

And it needn't be a terrorist attack. Open networks coupled with vulnerable software make it more likely that a transformational event will arise from a more banal source, like a motivated group of computer experts, a common thief or, most fickle of all, an accident.

The coming digital Pearl Harbour doesn't even have to be a single event. Thinking about the nature of disasters, Software Engineering Institute (SEI) fellow Watts Humphrey consulted nuclear power people. "I talked to one guy who did nothing but review incidents," Humphrey says. "And typically, these kinds of disasters result from a combination of many smaller events that each seem highly unlikely. But they all happen at once to create unforeseeable consequences."

That's the "Perfect Storm" theory, and what makes an event perfect (in a negative sense) is the apparent lack of relationship between systems in a complex environment. The blackout last August in the US was a Perfect Storm. Random, seemingly unrelated factors - an ageing power grid, certain corporate decisions, a heat wave, a history of deregulation and some human errors - all came together to darken a significant chunk of the northern hemisphere.

"That's how modern systems fail," says Humphrey. "And our networks are so big and fast that things which seem damn near impossible happen every few days."

Not even loss of life necessarily means an event is a digital Pearl Harbour. Three years ago, four Marines were killed after a hydraulics failure on a V22 Osprey plane. They took all the proper measures, but because of software bugs, their plane still crashed. Few even heard of the event, never mind demanded more secure software as a result.

Those scenarios, no matter how dire, didn't rise to the level of a Pearl Harbour because they failed to inflict significant, collective psychological damage. Before Internet security changes in fundamental ways, we will have to feel as shocked and vulnerable as all Americans did reading the newspaper and listening to the radio on the morning of December 7, 1941.

In a sense, this should be obvious. If digital Pearl Harbours were happening every day, they wouldn't be Pearl Harbours. They'd have a name that conveyed their seriousness, but also their ubiquity and survivability. They'd have a name like "virus outbreaks".

Still, no matter how nebulous the name, we're hurtling toward what many experts keep referring to, darkly, as the "point".

"The more complex you get, the more vulnerable you are," says Peter Tippett, CTO of TruSecure, a security services company, and noted security expert. Tippett argues that if we simply extend the present situation into the future, the level of complexity and vulnerability we would create will make a digital Pearl Harbour inevitable - and before 2010.

"For seven years, we've had these negative events," says Howard Schmidt, vice president and CISO of eBay and former vice chairman of the President's Critical Infrastructure Protection Board, and, before that, CSO of Microsoft. "And every time there's an event, it's called a wake-up call. It's like those alarms that crescendo to wake you up. We're getting to that point, where it's so loud, you wake up."

»TIPPING POINT: On December 7, 2008, computer systems around the world go down simultaneously. They do not come back up.