Updated at 2:11 p.m. ET
Hackers rushed to the defense of WikiLeaks on Wednesday, launching attacks on MasterCard, Swedish prosecutors, a Swiss bank and others who have acted against the site and its jailed founder Julian Assange.
So-called "hacktivists" operating under the label "Operation Payback" claimed responsibility in a Twitter message for causing severe technological problems at the website for MasterCard, which pulled the plug on its relationship with WikiLeaks a day ago.
"MasterCard rules prohibit customers from directly or indirectly engaging in or facilitating any action that is illegal," spokesman Chris Monteiro told CBSNews.com's sister site CNET.
MasterCard acknowledged "a service disruption" involving its Secure Code system for verifying online payments. It was not clear how widespread the problem was. Earlier, MasterCard spokesman James Issokson said consumers could still use their credit cards for secure transactions.
MasterCard is the latest in a string of U.S.-based Internet companies - including Visa, Amazon.com, PayPal Inc. and EveryDNS - to cut ties to WikiLeaks in recent days amid intense U.S. government pressure.
CBSNews.com Editor-in-Chief Dan FarberTuesday that the U.S. government had effectively "declared war" on WikiLeaks and its Australian founder, who was still Wednesday after surrendering the previous day to British police on a Swedish warrant for alleged rape.
White House press secretary Robert Gibbs told Fox News last week, "We are stronger than one guy with one website. We should never be afraid of one guy that plopped down $35 and bought a Web address. ... We're not scared of one guy with one keyboard and a laptop."
So far, says Farber, that "one guy" has been denied bail in the U.K., his website has been slammed by a series of covert and overt attempts by governments and businesses around the world (including MasterCard's) to cut off its oxygen supply, but the efforts have not stopped the information flow.
Visa said it was having no problems Wednesday. PayPal said it faced "a dedicated denial-of-service attack" for about half an hour Monday but had no problems with its website Wednesday.
The online attacks are part of a wave of support for WikiLeaks that is sweeping the Internet. Twitter was choked with messages of solidarity for the group, while the site's Facebook page hit 1 million fans.
One analyst has suggested WikiLeaks' hacker allies would be unable to inflict serious damage to companies or organizations that oppose the controversial whistleblower site.
"It would cost them a lot of money. They are more likely to temporarily increase the flow of traffic to these companies' websites, which would increase their costs but would not seriously disrupt normal services," Tony Dyhouse, an expert who advises the British intelligence services on cyber security told the EUobserver earlier this week.
"Currently the largest numbers of compromised machines lie in the hands of organized crime, because they are used for phishing [identity theft] and spam," said Dyhouse, who works for British think-tank Digital Systems Knowledge Transfer Network. "Over the past six years or so, organized crime has hired all the best hackers. Organized crime got into the game when they realized how much money they could make."
Offline, the organization is under pressure on many fronts. Assange is in a British prison fighting extradition to Sweden over a sex crimes case. Moves by Swiss Postfinance, MasterCard, PayPal and others that cut ways to send donations to the group have impaired its ability to raise money.
Undeterred, WikiLeaks released more confidential U.S. cables Wednesday. The latest batch 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 he would be released in 2009 on compassionate grounds.
Another cable revealed that American officials lobbied the Russian government to amend a financial bill the U.S. felt would "disadvantage U.S. payment card market leaders Visa and MasterCard."
Yet another U.S. memo described German leader Angela Merkel as the "Teflon" chancellor, but she brushed it off as mere party chatter. It also called her risk-averse and seldom creative.
The pro-WikiLeaks vengeance campaign appeared to be taking the form of denial-of-service attacks in which computers are harnessed - sometimes surreptitiously - to jam target sites with mountains of requests for data, knocking them out of commission.
PayPal Vice President Osama Bedier said the company froze WikiLeaks' account after seeing a letter from the U.S. State Department to WikiLeaks saying that its activities "were deemed illegal in the United States."
"It's honestly just pretty straightforward from our perspective," he said at a web conference in Paris.
More on WikiLeaks
Julian Assange Arrested in UK, Denied Bail
Swiss Cut Off WikiLeaks' Bank Account
WikiLeaks' Swedish Servers May Be Under Attack
Video: Julian Assange's Life on the Run
WikiLeaks' Assange May Seek Swiss Asylum
Neither WikiLeaks nor Assange has been charged with any offense in the U.S., but the U.S. government is investigating whether Assange can be prosecuted for espionage or other offenses. Assange has not been charged with any offenses in Sweden either, but authorities there want to question him about the allegations of sex crimes.
Per Hellqvist, a security specialist with the firm Symantec, said a network of web activists called Anonymous - to which Operation Payback is affiliated - appeared to be behind many of the attacks. The group, which has previously focused on the Church of Scientology and the music industry, is knocking offline websites seen as hostile to WikiLeaks.
"While we don't have much of an affiliation with WikiLeaks, we fight for the same reasons," the group said in a statement. "We want transparency and we counter censorship ... we intend to utilize our resources to raise awareness, attack those against and support those who are helping lead our world to freedom and democracy."
The website for Swedish lawyer Claes Borgstrom, who represents the two women at the center of Assange's sex crimes case, was unreachable Wednesday.
The Swiss postal system's financial arm, Postfinance, which shut down Assange's bank account on Monday, was also having trouble. Spokesman Alex Josty said the website buckled under a barrage of traffic Tuesday.
"Yesterday it was very, very difficult, then things improved overnight," he told the AP. "But it's still not entirely back to normal."
Ironically, the microblogging site Twitter - home of much WikiLeaks support - could become the next target. Operation Payback posted a statement claiming "Twitter you're next for censoring Wikileaks discussion."
Some WikiLeaks supporters accuse Twitter of preventing the term "WikiLeaks" from appearing as one of its popular "trending topics." Twitter denies censorship, saying the topics are determined by an algorithm.
Meanwhile, the French government's effort to stop a company from hosting WikiLeaks has failed - at least for now.
The Web services company OVH, which says a client hosts the wikileaks.ch website, sought a ruling by two courts about the legality of hosting WikiLeaks in France. The judges said they couldn't decide right away on the highly technical case.
WikiLeaks angered the U.S. government earlier this year when it posted a video showing U.S. troops gunning down two Reuters journalists. Since then, the organization has leaked some 400,000 classified U.S. war files from Iraq and 76,000 from Afghanistan that U.S. military officials say contained information that could put people's lives at risk.
The latest leaks involve private U.S. diplomatic cables that included frank U.S. assessments of foreign nations and their leaders. Those cables have embarrassing U.S. allies, angered rivals, and reopened old wounds across the world. U.S. State and Defense department officials say foreign powers have curtailed their dealings with the U.S. government since the documents hit the Internet.
U.S. officials have directed their ire at Assange but even some American allies have begun to ask whether Washington shares the blame.
"The core of all this lies with the failure of the government of the United States to properly protect its own diplomatic communications," Australian Foreign Minister Kevin Rudd said Wednesday. "To have several million people on their distribution list for a quarter of a million cables - that's where the problem lies."
Assange, meanwhile, faces a new extradition hearing in London next week where his lawyers say they will reapply for bail. The 39-year-old Australian denies two women's allegations in Sweden of rape, molestation and unlawful coercion, and is fighting his extradition to Sweden.
In a Twitter message Wednesday, WikiLeaks spokesman Kristinn Hrafnsson shrugged off the challenges and noted that the site still releasing documents and is mirrored by supporters in over 500 locations.
"We will not be gagged, either by judicial action or corporate censorship ... WikiLeaks is still online," Hrafnsson said.