Screen shot 2010 12 07 at 10.34.5311 300x251 Anonymous Operation : Payback campaign defends Wikileaks, downs MasterCard websiteOnline supporters of whistleblowing website Wikileaks are fighting back after news of Julian Assange’s arrest hit the wires.

Online activists known as “Anonymous” have initiated what they called Operation:Payback, a call to action to bring down the websites of companies that have publicly removed services once used by the Wikileaks website.

Anoymous has already targeted the Swiss bank PostFinance, a bank that froze all payments to the controversial website, after it promised to take down PayPal, the online payment company that cancelled Wikileaks’ account that it used to solicit donations.

Its current target? Mastercard. The website is currently down for a large number of users after a DDOS attack.

All of the groups actions have been publicly posted to the Anon_Operation Twitter account; the Paypal attack was posted to Twitter on December 6, declaring “target: www.paypal.com is YOYOing. Keep firing your lazors!”, the PostFinace attack was declared 17 hours ago and just minutes ago it was confirmed by the group that Mastercard had been taken offline as a result of its online assault.

Anonymous is a collection of online activists formed from popular online message boards, attacks are not for profit but are in most cases to demonstrate a show of force to promote unfair practises or highlight sensitive political issues. The three attacks here could just be the start of an uncomfortable few hours for the companies involved.