The Mastercard website is down, following an attempt by the Anonymous group at 4Chan to punish the company for its treatment of Wikileaks.
On Monday, Mastercard withdrew the ability to make donations to Wikileaks, as did Paypal on Saturday and VISA yesterday.
Anonymous says on its website that it has "declared war on the entities involved in censoring there [sic] information", and is now claiming to have brought down the Mastercard website. www.mastercard.com/ through a distributed denial of service (DDoS) attack.
It's posted this message on Twitter: "WE ARE GLAD TO TELL YOU THAT http://www.mastercard.com/ is DOWN AND IT'S CONFIRMED! #ddos #wikileaks Operation:Payback(is a bitch!) #PAYBACK".
Anonymous has also succeeded in shutting down the website of the bank that froze founder Julian Assange's assets. The PostFinance website has been unavailable for over 24 hours.
The move follows a similar attack on PayPal, which over the weekend announced it was to cease processing payments to Wikileaks. Anonymous wasn't able to bring the main site down, but pulled the blog offline for some time.
The VISA website remains functional - for the time being, at least. Other targets may include EveryDNS.net, which suspended its service to Wikileaks late last week, and Amazon, which stopped hosting Wikileaks content last Wednesday.
Meanwhile, the company that processes payments for Wikileaks, Datacell, says it plans a legal challenge to Visa and Mastercard over their decision not to process payments.
"DataCell ehf, who facilitates those payments towards Wikileaks, has decided to take up immediate legal actions to make donations possible again," says CEO Andreas Fink. "It is obvious that Visa is under political pressure to close us down."