LONDON — A dual Israeli-British citizen appeared in court on Thursday after being extradited from Germany for allegedly launching cyber attacks against two of Britain’s best known high-street banks and attempting to blackmail them.

Daniel Kaye, 29, allegedly orchestrated so-called distributed denial of service (DDoS) attacks, having developed software that allowed him to control up to 1.5 million computers all over the world that could then be used to overwhelm the target system with a barrage of communication. He has already been given a suspended sentence in Germany for similar crimes.

The attack is estimated it cost Lloyds £190,000 ($244,000, 206,000 euros) and Barclays around £146,000.

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Kaye, from Egham, Surrey, faced nine charges under the Computer Misuse Act as he appeared at Westminster Magistrates’ Court. He was remanded in custody until his next hearing.

Services at Lloyds and Barclays banks were disrupted by the cyber attacks in January, the National Crime Agency said in a statement following a joint investigation with Germany’s federal crime bureau BKA.

The attack on Lloyds Banking Group lasted three days and prevented some customers using their online accounts, although a bank spokeswoman said that no customer details or accounts were compromised.

Kaye also faces a charge that he “endangered human welfare” with an alleged cyber attack against Lonestar MTN, Liberia’s biggest internet provider, the NCA said in a statement on Wednesday.

“The investigation leading to these charges was complex and crossed borders,” said Luke Wyllie, senior operations manager at the NCA.

“Cyber crime is not victimless and we are determined to bring suspects before the courts,” he said.

On Wednesday Kaye was extradited from Germany on a European arrest warrant after being given a suspended sentence in that country for a massive cyber attack against Deutsche Telekom last year.

The regional court in the western city of Cologne said Friday it would suspend the sentence of one year and eight months against Kaye, following pleas to this effect by both prosecutors and the defence.

Kaye last week described as “the worst mistake of my life” the attack that knocked more than one million German households offline in November, carried out for money on behalf of a Liberian client.

He was detained in February at London’s Luton airport on a European arrest warrant for attempted computer sabotage and extradited to Germany.

German police said the goal of the attack was to infect users’ computers with a “botnet” — a network of web-connected machines that can be manipulated with malware and used to assault other online targets.

Kaye told the court he was paid $10,000 (about 8,500 euros) by a Liberian telecom company which wanted to use the botnet to damage local rival Lonestar MTN.

The attack, which the company said caused about two million euros of damage, ended when it advised customers to disconnect their routers and restart them after a software update.

The large-scale strike fuelled concerns over cyber security in Germany and officials have warned that more online assaults are possible ahead of a general election in September.

Times of Israel staff contributed to this report.