Christopher Weatherhead, a 22-year-old British student, has been convicted for taking part in cyber-attacks carried out by Anonymous.
He and three others were arrested over attacks on Paypal, Mastercard, Visa and the BPI as part of "Operation Payback".
Denial of service (DDoS) attacks were carried out against the companies rending their websites replaced by a message reading "You've tried to bite the Anonymous hand. You angered the hive and now you are being stung."
Despite denying an integral role in the attacks, Weatherhead was convicted of conspiracy to impair the operation of computers under the Criminal Law Act 1977.
Three others were also charged - Peter Gibson, 24, Ashley Rhodes, 28, and Jake Birchall, 18 – who all pled guilty at earlier hearings.
A sentence is yet to be passed down with Judge Peter Testar explaining, "I want to have as much information as possible before deciding what should happen in the case of these four men.
"I think these are serious offences to my mind, and I hope the defendant understands that."
From The Guardian