REVENGE: Thirteen people admit to the December 2010 cyber attack on PayPal over the suspension of WikiLeaks' accounts.

A group of 13 defendants who had been charged in a cyber attack on PayPal's website pleaded guilty and admitted to the December 2010 attack over PayPal's suspension of WikiLeaks accounts.

The pleas took place in a California federal court on Thursday and were announced on Friday by the US Attorney's Office in San Francisco.

Following the release of a large amount of classified documents by WikiLeaks, PayPal suspended its accounts so that the anti-secrecy website could no longer receive donations. In retribution, the group "Anonymous" coordinated and executed denial-of-service attacks against PayPal.

The group of defendants who pleaded guilty were composed of 11 men and two women. Ten of them pleaded to a felony charge, but will be allowed to change that to a misdemeanour next year if they do not violate terms of their agreement before sentencing, according to the US attorney's statement.

The three other defendants agreed to misdemeanour charges.

eBay's PayPal unit is a service that facilitates the electronic transfer of money between parties.