Searches have been carried out at an address in Bradford as part of an international investigation into a website linked to millions of cyber attacks around the globe.
The National Crime Agency (NCA) today said that the search was carried out as authorities in five countries targeted six members of a gang behind the webstresser.org website.
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Action has taken place in countries including the Netherlands, Serbia, Croatia and Canada.
The website, which was used in attacks on some of the UK's biggest banks, has also been shut down.
It is believed that a person linked to the Bradford address had used the site to target seven banks last year.
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An NCA spokesman said: "Criminals across the world have used webstresser.org, which could be rented for as little as 14.99 US dollars, to launch in excess of four million so-called distributed denial of service (DDOS) attacks, in which high volumes of internet traffic are launched at target computers to disable them.
"Individuals with little or no technical knowledge could rent the webstresser service to launch crippling DDOS attacks across the world.
"As part of the operational activity, an address was identified and searched in Bradford and a number of items seized.
"NCA officers believe an individual linked to the address used the webstresser service to target seven of the UK's biggest banks in attacks in November 2017.
"They were forced to reduce operations or shut down entire systems, incurring costs in the hundreds of thousands to get services back up and running."