A cybercriminal who targeted hundreds of millions of computers with ransomware has been jailed for nearly six and a half years following an investigation by the National Crime Agency (NCA).

Described by the NCA as a ‘top-level cyber criminal’, Zain Qaiser of Barking, Essex, was a member of an international organised crime group that preyed upon victims in more than 20 countries.

An investigation found that the computer science student made more than £700,000 for his role in a global malware and blackmail campaign. However, the NCA said that the total amount he made from cybercrime activities is likely to be “very much higher”.

Buying “masses of advertising traffic” from pornographic websites using the online name K!NG, Qaiser posed as a legitimate online advertising agency as part of a social engineering ploy.

Once advertising was secured, Qaiser, on behalf of the crime group, would host and post advertisements laced with malicious software.

Users who clicked on the ads were redirected to another website which hosted sophisticated malware strains, including the infamous Angler Exploit Kit (AEK). Users with vulnerabilities would be infected with a malicious payload.

One particular payload, the NCA said, was a piece of software known as Reveton, which is designed to lock a user’s browser.

Users locked in by the malware would be met with a message purporting to be from a law enforcement or government agency informing them that an offence had been committed. Victims were told they would have to pay a fine ranging between $300-$1000 in order to unlock their device.

Ransom demands were made through a process of virtual and cryptocurrency money laundering, the NCA said. Blackmailed victims would be forced to pay a ransom in a currency chosen by Qaiser and his associates.

Commenting on the conviction, NCA Senior Investigating Officer Nigel Leary said: “This was one of the most sophisticated, serious and organised cybercrime groups the National Crime Agency has ever investigated.

“The group owned and operated the Angler Exploit Kit – one of the most successful and closely guarded pieces of malicious software ever developed by the cybercrime community.”

Leary added: “Zain Qaiser was an integral part of this organised crime group generating millions of pounds in ransom payments by blackmailing countless victims and threatening them with bogus police investigations.

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Online advertising agencies, which discovered Qaiser’s criminal activities tried to stop him. However, a number of businesses and individuals were subsequently blackmailed – with two agencies being hit with DDoS attacks.

Qaiser told one company director: “I’ll first kill your server, then send child porn spam abuses.”

These attacks resulted in companies losing at least £500,000 through lost revenue and mitigation costs.

“When Qaiser’s criminal enterprise was frustrated by diligent members of the online advertising community, he retaliated causing misery and hundreds of thousands of pounds in financial losses,” said Leary.

Qaiser admitted 11 offences, including blackmail, fraud, money laundering and computer misuse. He was jailed at Kingston Crown Court.