A teenager who hacked into an American government laboratory's computer network could face a £21,000 bill.
McElroy is a first-year university student
Joseph McElroy, 18, from east London, wanted to use its power to download films and music from the internet.
But his intrusion sparked a full-scale alert at the Chicago laboratory, which researches high-energy particles.
Bow Street Magistrates' Court was told the US government wants compensation to cover the costs of repairs after officials "pushed the panic button".
McElroy has admitted developing a sophisticated computer programme to break into 17 computers at the Fermi National Accelerator Laboratory, near Chicago, in June 2002.
The Exeter University student, from Woodford Green, also admitted unauthorised modification of a computer at a previous hearing.
Stuart Sampson, prosecuting, told the court on Thursday: "The panic button was pushed due to the uncertainty.
"Initially the United States took this matter very seriously because of the nature of the laboratory."
He said the US government estimated the cost of repairs, largely those of manpower hours, at £21,000.
Because of the large sum sought, district judge Daphne Wickham referred the case to Southwark Crown Court.
McElroy was granted bail and told he would be sentenced in the New Year.