U.S.-based companies including Mastercard, Visa and PayPal have cut ties with WikiLeaks, refusing to process donations to the controversial site. The anonymous "hacktivists" are calling their cyber war "Operation Payback." The supporters of WikiLeaks have launched spam attacks that are causing the company sites to crash.
The hackers are using a modified version of software generally used to conduct "stress testing" on websites, according to Paul Mutton, an analyst with the London-based company Netcraft, which is tracking the attacks.
The technique allows even unsophisticated supporters to participate in attacks because all they have to do is download the file, which is then remotely operated to send a stream of bogus page requests to target websites.
Also among the sites apparently being hacked is Sarah Palin's political action committee website. Palin has been a harsh critic of WikiLeaks.
Meanwhile, Assange remains in a British prison, fighting extradition to Sweden to face charges for rape and sexual molestation.
Russia's prime minister on Thursday used the WikiLeaks founder's arrest to suggest that the West has issues with democracy. In leaked U.S. cables, Russia was described as undemocratic and corrupt.
The Associated Press contributed to this report.