Around 350,000 PCs – 20,000 in the UK – are infected with an invisible, undetectable Trojan computer virus called DNSChanger, which sends web users to unintended and sometimes illegal websites.

The FBI set up surrogate servers to keep the PCs working, but it’s costing the body so much they intend to cut the users connections on July 9.

The servers were set up to give companies the time to remove the Trojan, which was traced back to a crime ring in Estonia, from their infected servers.

Agent Tom Grasso told Fox News: “If we just pulled the plug on their criminal infrastructure, the victims were going to be without internet service.”

The Trojan sends users to web pages controlled by the gang, who have received an estimated £9.1 million in commission from adverts on the sites, since the scam started in 2007.

The virus is particularly effective because it stops users from visiting secure sites that could help them stop it.

Law enforcement officers and computer companies have been working together to fight the bug.

Six men were charged over the internet fraud scheme, which has affected people in over 100 countries.