Nine out of every 10 large corporations and government agencies have been attacked by computer intruders.

I went from being a kid who loved to perform magic tricks to becoming the world's most notorious hacker, feared by corporations and the government.

I was addicted to hacking, more for the intellectual challenge, the curiosity, the seduction of adventure; not for stealing, or causing damage or writing computer viruses.

Most of the computer compromises that we hear about use a technique called spear phishing, which allows an attacker access to a key person's workstation. It's extremely difficult to defend against.

Think about it: if you were running a multi-million dollar company, and your database of customer information was stolen, would you want to tell your clients? No. Most companies did not until the laws required them to. It's in the best interest of organisations - when they're attacked and information is stolen - to tell nobody.

Social engineering is using deception, manipulation and influence to convince a human who has access to a computer system to do something, like click on an attachment in an e-mail.