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main routes into third-party computers. They were digital holes in the armour of software and computer systems, which the manufacturer had failed to spot. Once a company like Microsoft or Adobe noticed that a hacker had penetrated Windows or a ubiquitous application like PDF Reader by using a particular vulnerability, it was then able to close it or 'patch it' by writing a specific security fix, as it is known. Next, it would alert its customers to download the fix and install it, thus blocking that route into the customer's computer. If the user failed to update the fix, the computer could still fall foul of a virus exploiting that particular vulnerability, should it come calling.

Super security hackers like Vision would often spot vulnerabilities before anybody else and so, in the spirit of good neighbourliness, he offered practical advice to users on how to protect themselves.

But his good deeds went further. He also gave his services free of charge to the FBI station in San Francisco, and the Feds were only too happy to accept the help.

No challenge on the Web was too great for Max Vision, no vulner- ability too small for him to spot. But of course in order to seek out those vulnerabilities, he needed to probe computer systems all the time. He knew this put him at the centre of a profound dilemma that affected the computing industry with serious ramifications. In order to protect yourself from criminal or 'blackhat' hackers, it was sometimes necessary as a 'whitehat' hacker to ascertain how to break into systems – an act that might in itself have been illegal.

It is almost unavoidable for 'whitehats' to sniff around large public computer systems, just as 'blackhats' do. The difference is that the 'whitehats' will not exploit for personal gain any vulnerability they find. The 'blackhats' probably will.

Operating out of the little house he shared with Kimi, Vision found that whenever he came across a network anomaly or problem, he could not resist the urge to correct it. In 1998 he discovered a dangerous vulnerability on the networks serving a series of government agencies, including parts of the Pentagon. This was a hole in their defences through which all manner of mischievous worms could wriggle. Liter- ally hundreds of thousands of government computers could be compro- mised by skilled hackers working anywhere in the world. Again demonstrating his patriotic commitment, Vision filled these holes with digital cement to ensure the security of his nation: nobody would be

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