Assange denies the charges.
Hackers attacked websites for the attorneys prosecuting Assange, as well as the Swiss authority that froze his bank account and MasterCard, which announced on Tuesday it would no longer process donations to WikiLeaks.
The online vengeance campaign, under the label "Operation Payback", 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.
The hackers disrupted websites for Visa and MasterCard, causing big problems on the companies' websites.
Former vice-presidential candidate Sarah Palin, who has been critical of Assange, has also run into problems.
She told ABC News hackers disrupted her personal credit card accounts and tried to shut down her website.
The online attacks are part of a wave of online support for WikiLeaks that is sweeping the Internet. Twitter was choked with messages of solidarity Wednesday, while the site's Facebook page hit 1 million fans.
In the meantime, the U.S. government is investigating whether Assange can be prosecuted for espionage.
Those cables have had serious repercussions for the United States, embarrassing allies, angering rivals, and reopening old wounds across the world.
Foreign powers have been pulling back from their dealings with the U.S. government since the documents hit the Internet, State and Defense department officials said Tuesday, while the Israeli government complained that the crisis over the leaked files was distracting Washington from efforts to restart Mideast peace talks -- something Washington has denied.
The latest U.S. cables released Wednesday showed that the British government feared a furious Libyan reaction if the convicted Lockerbie bomber wasn't set free and expressed relief when they learned that he would be released in 2009 on compassionate grounds.
The Associated Press contributed to this story.