But then the so-called "hackivists" took their own cyber shots as several websites they were apparently using to organize the attacks, including Facebook and Twitter, were also taken down. The FBI is investigating the so-called Operation: Payback attacks, U.S. Attorney General Eric Holder said in a press conference today.
A cached page for Anonops.net, a page that is currently down but had shown Anonymous' alleged plans, quotes the co-founder of the Electronic Frontier Foundation, which describes itself as the "first line of defense" against attacks on online freedom.
"The first serious infowar is now engaged. The field of battle is WikiLeaks. You are the troops," EFF co-founder John Perry Barlow said in a tweet last week.
Wikileaks spokesperson Kristinn Hrafnsson told ABC News in an exclusive interview the refusal of service by Mastercard, Visa and Paypal amounted to an "outrageous" attack on freedom of speech.
"We are seeing growing support for us, especially in the last few days when we've had these outrageous attacks on us by companies that are bowing to political pressure from political forces in the United States," Hrafnsson said Wednesday. "We are getting seriously close to censorship in the United States and that must surely go against the fundamental values that the country is based upon."
One of the most recent cables leaked to anger U.S. authorities includes a list of installations vital to America's national security and interests.
U.S. Defense Secretary Robert Gates, in remarks to reporters Tuesday from Afghanistan, said Assange's arrest is "good news."
U.S. government officials say that the diplomatic leaks have already had an effect on relationships with individuals and governments around the world.
"We have gotten indications that there is at least some change in how individuals and governments cooperate with us, and share information," said Pentagon spokesman Col. Dave Lapan, without providing any details. There's a vague "sense that there has been some pulling back because of these revelations."
Speaking a press conference Monday, Secretary of State Hillary Clinton said the leak could "create potential dangers for our friends and partners."
In a February 2009 cable, American envoys were asked to identify sensitive places "whose loss could critically impact the public health, economic security, and/or national and homeland security of the United States."
Clinton said she would not comment on "any specific cable," but said the theft of the cables was "deeply distressing."
Clinton then called on "countries around the world and businesses to assist us in preventing any of the consequences that could either endanger individuals or other interests internationally."
Though Assange has not been arrested on charges relating to the released cables, U.S. Attorney General Eric Holder said the release of the documents had put the United States at risk and said he authorized a criminal investigation into Assange.
"The national security of the United States has been put at risk; the lives of people who work for the American people has been put at risk; the American people themselves have been put at risk by these actions that are, I believe, arrogant, misguided and ultimately not helpful in any way. We are doing everything that we can," Holder said.
"We have a very serious, active, ongoing investigation that is criminal in nature. I authorized just last week a number of things to be done so that we can hopefully get to the bottom of this and hold people accountable, as they -- as they should be."