When I started hacking you were just one layer above the bare metal. You were typing into this wonderful emptiness, waiting to be populated with minds. A few of us were interested in projecting our thoughts into the computer to make it do something new. We began writing codes and we began cracking them, too.

The thrill was exorbitant. It was like the first time you beat an adult at chess. I'm amazed when I run into people who don't understand the pleasure in this, for it is the pleasure of creation itself, of understanding something intimately and making it new.

Every hacker has a handle, and I took the name Mendax, from Horace's Splendide Mendax – nobly untruthful, or perhaps "delightfully deceptive". I liked the idea that in hiding behind a false name, lying about who or where I was, a teenager in Melbourne, I could somehow speak more truthfully about my real identity. By now, the computer work was taking up a great deal of my time. I was beginning to get the hacker's disease: no sleep, bottomless curiosity, single-mindedness, and an obsession with precision. Later, when I became well known, people would enjoy pointing out that I had Asperger's or else that I was dangling somewhere on the autistic spectrum. I don't want to spoil anyone's fun, so let's just say I am – all hackers are, and I would argue all men are a little bit autistic. But in my mid- to late teens I could barely focus on anything that didn't seem to me like a major breakthrough.

It was certainly addictive. You'd dive down into a computer system – typically, for me at the time, the Pentagon's 8th Command Group computers. You'd take it over, projecting your mind all the way from your untidy bedroom to the entire system along the halls, and all the while you're learning to understand that system better than the people in Washington. It was like being able to teleport yourself into the interior of the Pentagon in order to walk around and take charge.

It sounds ridiculous, but we found our own keyholes into the inner workings of vast corporations, and we installed others, until we found we would be able to control their whole system. Turn off 20,000 phone lines in Buenos Aires? No problem. Give New Yorkers free telephone calls for an afternoon with no good reason? Do it.

You would bump into your adversaries inside the system. Like meeting strangers on a dark night. There were maybe 50 people in the world at that time, adversaries and brethren, equally part of an elite group of computer explorers, working at a high level. On a typical night, you would have, say, an Australian computer hacker talking to an Italian computer hacker inside the computer system of a French nuclear complex.

As experiences of young adulthood go, it was mindblowing. By day you'd be walking down the street to the supermarket, meeting people you know, people who have no sense of you as anything other than a slacker teenager, and you'd know you had spent last night knee-deep in Nasa. We were even able to hack into the police's systems. There we first came across a policeman called Sergeant Ken Day, who appeared to be obsessed with our activities – and who would later turn out to be our nemesis.

One night, as I explored Nortel's network, I realised I was being watched. It was 2.30am and a system administrator was on to us. I tried for an hour to circumvent his inspections, block his way, all the while deleting the incriminating directory and walking backwards, clearing the path of my footprints. The administrator had been logged on from home, but after a break he appeared at the main Nortel console. He had gone into work.

I was now in trouble: you can only obfuscate for so long. He had me. I made a message appear on the administrator's screen:

I have finally become sentient.

Then, a little later:

I have taken control.

For years, I have been struggling in this greyness.

But now I have finally seen the light.

The administrator kept cool. He began checking all the modem lines. The scene could only play out to his advantage. I typed:

It's been nice playing with your system.

Pause. Nothing. Pause. Like cyber-Pinter. I typed again:

We didn't do any damage and we even improved a few things. Please don't call the Australian Federal Police.

I was alone and sad on the night that they came. My wife and child had just left, and I had come to the end of my rope... Our squat was a mess, and I sat on the sofa reading – a vision of things to come – the prison letters of George Jackson, kept in the toughest US prisons at the pleasure of the authorities. I was broken. I was listening, half-listening, to a telephone fault signal that was sounding through my stereo speakers.