A computer hacker from the online activism group “Anonymous” was sentenced in Britain to 18 months in jail for conspiring to attack the websites of Visa Inc., PayPal Inc., MasterCard Inc. and others.

The prison term was handed down Jan. 24, according to a clerk at Southwark Crown Court in London. Christopher Weatherhead was found guilty in December, while three co-defendants -- Jake Birchall, Ashley Rhodes and Peter Gibson -- pleaded guilty earlier to conspiring to impair the operation of computers.

Britain’s Crown Prosecution Service described Weatherhead in December as a “cyber-criminal who waged a sophisticated and orchestrated campaign of online attacks” on computer systems.

Gibson was ordered to perform 100 hours community service and given a six-month suspended sentence for two years, meaning he faces jail if he offends again during that period. Birchall’s sentence will be discussed at a hearing scheduled for Feb. 1, the clerk said. Rhodes’s sentence hadn’t been discussed yesterday, the clerk said.

The four also targeted the British Recorded Music Industry, Ministry of Sound and the International Federation of the Phonographic Industry, prosecutors said. The attacks cost the companies more than 3.5 million pounds ($5.5 million) in extra staffing, software and sales losses.

U.K. police have been investigating “hacktivist” collectives Anonymous and LulzSec for conducting denial-of- service attacks, which flood computer networks with requests for information until they shut down.

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