This is the story of Zain Qaiser. A student who made hundreds of thousands of pounds blackmailing porn users with cyber attacks from his parents’ house in East London. He spent almost £5,000 on a Rolex watch, £2,000 on a stay in a Chelsea hotel and £70,000 in a shopping centre casino. Today he was jailed for more than six years.

But for every Zain there’s a Fabian. Fabian Wosar destroys the kind of ransomware that Zain Qaiser used to extort money. Fabian is so successful that cyber gangs leave threatening messages for him in their code to try and scare him off. The BBC’s Dominic Casciani and Joe Tidy take us into the murky world of cyber criminals and the hero hackers trying to stop them.

Producer: Duncan Barber