The hacker network, called Anonymous, brought down the Web sites of MasterCard, Visa, PayPal and the Swedish government in "Operation Payback" after the businesses severed ties with WikiLeaks and the Swedish government issued an arrest warrant against Assange on unrelated sexual assault allegations. Assange, in a London jail, denies the allegations, saying they're part of a smear campaign.
"They will go after the weakest links because they want to see results. They will probably test a few sites and then decide," Gregg Housh, a U.S. Internet activist who once worked with the hackers, told The Daily Telegraph in an interview published Friday.
Assange is scheduled to appear in magistrate's court Tuesday.
WikiLeaks, a whistle-blowing site, obtained and released for publication more than 250,000 U.S. State Department cables that included frank discussions about world leaders.
The sites so far hit by Anonymous were victims of "distributed denial of service" in which they were overloaded with "visitors," forcing them to crash.
One hacker told the Telegraph the operation is "definitely an information war."
"The core principle behind it is information is free, governments keep information to themselves, WikiLeaks releases it to the general public and the war occurs," the unnamed hacker said.