There was a time when hacking was something positive. It was done in the name of intellectual curiousity rather than financial reward.
By Mark Ward
BBC News Online technology correspondent
As such, it is something that Professor Neil Barrett is happy to admit that he used to do.
More criminals are planning crimes on computers
Dr Barrett's hacking days are long past and as technical director of computer security and forensics firm IRM, he is much more likely to be helping catch and convict hackers than join them.
But Dr Barrett has stayed a hacker in at least one sense.
Hacking was originally about being intimately familiar with a system and how it can be used and abused.
Nowadays Dr Barrett's familiarity is with the way that computers are used to commit hi-tech crimes and how they are used by people when committing other crimes.
This understanding extends beyond mere bits and bytes.
The book he has written, called Traces of Guilt, detailing his part in several high-profile cases, shows the emotional cost of dealing with the grim facts of investigating murder and child pornography.
The reason he was called in to help with such cases, said Dr Barrett, is that computers are now so ubiquitous that they are routinely used to plan and co-ordinate almost every crime.
Barrett: A lot of crime is going digital
This is a big change from the early days of his involvement with computer crime.
Back then it was a case of hi-tech tools for hi-tech crimes that contravened various parts of the Computer Misuse Act.
"Now," he said, "these things are automatically used by the criminal classes.
"The computer becomes their address book."
As a result, forensic examination of a suspect's computer is often key to cracking a case.
"It has become as important as protecting fingerprints and footprints and body fluid evidence at a murder scene," he said.
Anything that helps police build up a picture of a suspect's circle of contacts or what they were doing online or before the crime was committed can be enormously useful.
The growing use of computers has set a burden on the police to do a good job of handling the data on a PC.
It's all too easy, said Dr Barrett, to change the data on a PC and taint the chain of evidence that will be presented in court.
"A clumsy bobby will get the information but the important thing is to get the evidence," he said.
Hack and spend
Another trend that Dr Barrett has seen is the creeping criminality of hacking, much of which is now carried out for explicitly financial reward.
Some criminal hackers are threatening to bombard some web-based businesses with gigabytes of data unless large amounts of cash are handed over. It is extortion with a hi-tech gloss.
Many gambling websites have been hit by criminal hackers
In Dr Barrett's experience, many of these criminal hackers have full-time jobs in technology.
"Professional hackers are professional in all senses of the word," he said, "they work in the industry."
But, he adds, although there are some criminal hackers there is still a gap between them and other career criminals.
Many malicious or criminal hackers who profit by what they do fall down when trying to spend their ill-gotten gains.
"You can be the world's best hacker but I bet you do not know how to launder or hide the fact that you have got money," he said.
"For a professional crook the object of the exercise is not to get money. It is to spend money without going to prison and that's what hackers need to learn."
He believes that the gap between hackers and criminals is breaking down not least because cash stolen on the net is easy to get away with.
"Where's the money now? It's online," he said. "Now you can steal £1m and it weighs as much as an electron weighs."