Hackers, often children in developing countries using laptops in their bedrooms or computer hubs, are being paid vast sums of money for discovering weaknesses in foreign computer systems that can be exploited. After writing 21 novels featuring undercover intelligence operative Nick Stone during the past 24 years, with global sales of more than seven million copies, Bravo Two Zero hero McNab says it was time for a change.

Fans will get to meet his new character Nathan Pike in Shadow State, which was published on Thursday.

Pike is a gifted computer hacker who is not afraid to get his hands dirty, after learning to pick locks and crack safes as a wayward teenager. In the novel, Pike is sprung from a prison in Cambodia by the mysterious Melody Jones to go to El Salvador and steal $4billion in national reserves stored in the online currency Bitcoin.

So starts an adventure which also takes in Rwanda, Morocco and Dubai. The former SAS action man turned author, who never allows the whole of his face to be photographed or filmed to protect him from enemies made during undercover operations in Northern Ireland in the 1980s, says he is proud of his new creation and eager to gauge reader’s reactions.

McNab, not his real name, says about retiring Nick Stone in Down To The Wire last November: “If we had run it in chronological order I think he’d be about 180, so it felt like a natural progression to get to the point of, you know what, I’ve had enough of this.

“Nathan Pike is hopefully a bit different to just being a tech geek, in that he can do both worlds, so he can do the physical stuff of breaking in, which he learned to do as a kid.

“He knows how to get into somewhere, to get what he needs and get out without anybody knowing he’s been there.

“But also when he is there, he has the technical ability to manipulate the internet, so this is a perfect combination.

“Normally you have a guy who will break down the doors and a guy who will use a laptop to get the information, but he is both.” McNab was a wayward teenager himself after being brought up by adoptive parents in Peckham, south London.

As a baby he had been left in a hospital doorway in a Harrods carrier bag.

After turning to petty crime and a spell in borstal, he was saved by joining the Army where he learnt to read.

As a member of 22 SAS he was at the centre of covert global operations for nine years and was awarded the Distinguished Conduct Medal and Military Medal.

He became an author with his best-selling account of Brave Two Zero, a failed operation during the 1991 Gulf War that saw him taken prisoner and brutally tortured.

He left the SAS in 1993, the year Bravo Two Zero came out, and has since published more than 30 books.

McNab, now 63, speaking by phone with a “no-caller ID” from his home in New York City last week, said he has been interested in tech developments since being trained to deploy electronic counter-measures as an infantry soldier in the 1980s.

But he does not count himself as a computer expert, saya ing: “Maybe about four years ago I did a bit of Bitcoin, you know playing about with how it all works. I only came away with about £50, so not a huge amount.

“But what I am really fascinated about is this whole conflict that is constantly going on between the big powers – United States, China and Iran, and Russia.

“The biggest cyber attack ever took place during the pandemic on the US health system.

“The Iranians closed it down and basically they said America should stop shouting about Iran because their tongue will cut their throat. And this opened up the floodgates of a dam and America could not do anything about it.”

He adds: “The big players are looking to exploit zero days.

“These are things you can exploit in different software systems that nobody knows about, so you keep them and they are like holding a nuclear weapon.

“So, for example, with the Iranian zero-day which toppled the whole structure of the American health system, this left them having to use pencils and paper. So the Iranians exploited a weakness and it took huge effort to deal with it.” Contrary to the popular image of cyber attacks being orchestrated in shiny modern offices by smartly dressed university graduates, most of the computer malware like zero days are discovered by self-taught youngsters from poor backgrounds.

McNab says: “There are literally tens of thousands of people out there, often quite young and from developing countries as well, who find these exploits.

“It has become a huge industry and governments employ commercial entities to try and keep their infrastructure stable.

“GCHQ is constantly trying to stop it but they are also part of the war as well, getting out there to look for exploits as well.”

McNab is happy that he has reached a stage in his writing career where he no longer has to worry about his books being adapted for film or TV.

He says: “I spend my life having phone calls and going to lunches with people and actors who are going to do it.

“And you get to a point and it never happens.

“So now I don’t even bother turning up. I go ‘Look, if you want to do it, let’s do it’ but if not no problem, as it goes on and on. I am lucky enough to have had some success producing other people’s stuff in the States and if my own stuff comes up, then great, if it doesn’t then it does not really matter.”

• Shadow State (Welbeck, £16.99) is out now. To order a copy visit expressbookshop.com or call 020 3176 3832. Free UK P&P on any orders over £12.99

I haven’t read his books… and he wasn’t in SAS!

Despite a new wave of ex-special forces soldiers like Ant Middleton and Billy Billingham, now also writing thrillers, McNab says he does not see them as rivals.

He says: “There are so many out there now but I don’t really look at them as competition.”

And he laughed off a jibe by former SAS Who Dares Win chief instructor Middleton, 42, when promoting his latest book last November, that he was “better than Andy McNab”, saying: “Well he might be if he was ever in the SAS, but he wasn’t, was he! He was a Marine.

“I haven’t read any of his books.”