Mastercard is having severe technical problem Wednesday, Dec. 8, 2010, possibly a target by supporters of WikiLeaks founder Julian Assange.(Mark Lennihan, file/ Associated Press)

Supporters of WikiLeaks have launched cyber-attacks on the perceived enemies of founder Julian Assange, including MasterCard, PayPal, and the Swiss authority that froze Assange's bank account.

Several credit card and online payment companies, including Visa and PayPal, announced they would stop processing payments to WikiLeaks this week.

The online vengeance campaign appeared to be taking the form of denial of service attacks in which computers across the Internet are harnessed -- sometimes surreptitiously -- to jam target sites with mountains of requests for data, knocking them out of commission.

MasterCard's website seemed to be having severe problems Wednesday and service was disrupted. PayPal was also targeted several times, but managed to maintain its payment processing, the Guardian reports.

Amazon.com, which removed WikiLeaks' material from its server, and Visa, could also be possible targets.

With files from The Associated Press

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