Hackers rushed to the defense of WikiLeaks on Wednesday, launching a new attack on Visa after shutting down MasterCard, Swedish prosecutors, a Swiss bank and others who have acted against the site and jailed founder Julian Assange.
Internet "hacktivists" operating under the label "Operation Payback" claimed in a Twitter message, "we are attacking www.visa.com in an hour! Get your weapons ready and stay tuned," NBC News reported.Red Tape: WikiLeaks vigilante war spills onto Web
At 4 p.m. ET, the group tweeted: "TARGET: WWW.VISA.COM :: FIRE FIRE FIRE!!! WEAPONS."
Visa's corporate site, Visa.com, became unavailable to many users Wednesday. "Visa's corporate site - Visa.com - is currently experiencing heavier than normal traffic. The company is taking steps to restore the site to full operations within the next few hours," according to a Visa statement, NBC News reported.
But a Visa official told NBC News that its processing network, which handles cardholder transactions, was operational and account data was not at risk.
The group also claimed responsibility for hacking the website and personal information of former Gov. Sarah Palin. "No wonder others are keeping silent about Assange's antics. This is what happens when he is exposed and you exercise your First Amendment rights and speak up against Assange's sick, un-American espionage efforts," Palin said in an email to NBC News.
But Operation Payback itself appeared to run into problems, with many of its sites went down. It was unclear who was behind the counterattack.
Facebook banned the group from the social networking site Wednesday afternoon. "We take our Statement of Rights and Responsibilities very seriously and react quickly to reports of inappropriate content and behavior," according to the Facebook statement, NBC News reported.
Twitter also reportedly blocked Operation Payback's account, NBC News reported.
Earlier in the day, hackers claimed to have taken down MasterCard's website in retaliation for the company's decision to cut off services to WikiLeaks. The group had tweeted a link to hundreds of apparently leaked Mastercard credit card numbers, according to NBC News.
"WE ARE GLAD TO TELL YOU THAT http://www.mastercard.com/ is DOWN AND IT'S CONFIRMED!," anti-censorship group Anonymous said in a post to its Twitter site for an initiative it has dubbed Operation Payback.
In MasterCard attack, attempts to load the site Wednesday were unsuccessful. A spokesman for the company told msnbc.com that it did not have any information or comment at this stage.
The group has also claimed responsibility for distributed denial-of-service (DDoS) attacks on the website of the Swedish prosecutor's office that is pursuing the WikiLeaks founder for alleged sex crimes, PayPal and the Swiss bank that froze Assange's assets, the BBC reported.
The office of the lawyer representing Assange's two accusers in Sweden also told NBC News Wednesday that its website was inaccessible due to hacker attacks.
WikiLeaks tweeted a statement on Wednesday addressing Assange's arrest and noting efforts to cut off the flow of money to WikiLeaks.Video: Assange vows to fight extradition (on this page)
"We will not be gagged, either by judicial action or corporate censorship. Today Visa joined MasterCard, Paypal, Amazon, EveryDNS and others in cutting off their links," spokesman Kristinn Hrafnsson said in a statement.
"Wikileaks is still online. The full site is duplicated in more than 500 locations. Every day, the cables are loaded more than 50 million times," he added.
Anonymous said on its website that while it doesn't have a formal relationship with WikiLeaks, the two organizations shared the same ideals.
"We will find and will attack those who stand against Wikileaks and we will support WikiLeaks in everything they need," the site said, noting that Operation Payback would include providing a mirror for the WikiLeaks site, creating "counter-propaganda" and "organizing attacks (DDoS) on various targets related to censorship."
Assange speaks out
Meanwhile, Assange defended his secrets-spilling website in an editorial published in an Australian newspaper, a day after he was arrested in London in a sex-crimes investigation.
In the editorial, published by The Australian, Assange writes that there is a great need for WikiLeaks and denies that the site's publication of classified information has endangered lives.
"WikiLeaks has a four-year publishing history. During that time we have changed whole governments, but not a single person, as far as anyone is aware, has been harmed," Assange wrote. "But the US, with Australian government connivance, has killed thousands in the past few months alone."Video: Assange loyalists wage Wiki-war (on this page)
The WikiLeaks statement on Twitter also addressed Assange's arrest in Britain on Tuesday.
"Today, Wikileaks editor-in-chief Julian Assange was refused bail by a UK court ... However, this will not stifle Wikileaks," Hrafnsson said. "The release of the US Embassy Cables — the biggest leak in history — will still continue. This evening, the latest batch of cables were released, and our media partners released their next batch of stories."
The Frontline Club, a journalism organization based in London, said Wednesday that Assange "has spent much of the last several months working from our facilities," and that the club's founder offered Assange "an address for bail."
It is unclear why Assange did not provide a U.K. address during his initial court appearance; he instead provided an Australian one. In denying bail, the judge at Tuesday's hearing said there were "substantial grounds" to believe Assange could flee if granted bail.
Assange faces a new extradition hearing next week, in which his lawyers say they will reapply for bail.
In his editorial, Assange wrote that democracies require strong media to keep governments honest and that WikiLeaks helps fulfill that role. "WikiLeaks has revealed some hard truths about the Iraq and Afghan wars, and broken stories about corporate corruption."
The 39-year-old Australian surrendered to British officials Tuesday to answer a warrant issued for his arrest by Sweden. He is wanted for questioning after two women accused him of having sex with them without a condom and without their consent.
Assange's lawyers say the accusations stem from a "dispute over consensual but unprotected sex" and say the women only made the claims after finding out about each other's relationships with Assange.
'Presumption of innocence'
In Australia, a senior lawmaker blamed the United States, not its native Assange, for release of about 250,000 secret cables.
Foreign Minister Kevin Rudd told reporters in Brisbane Wednesday that Australia would support Assange as it would any Australian arrested abroad.
"Any Australian citizen is entitled to the presumption of innocence — and that includes Mr. Assange," Rudd said.
Later, Rudd was quoted as saying the leaks raised questions over the "adequacy" of U.S. security over the cables.
"Mr. Assange is not himself responsible for the unauthorized release of 250,000 documents from the U.S. diplomatic communications network," Rudd told Reuters in an interview.
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"The Americans are responsible for that," said Rudd.
During his court appearance, Assange said he would fight extradition to Sweden and he provided the court with an Australian address.
Britain's Sky News reported that Assange was receiving consular assistance from officials at the Australian High Commission.
The next court hearing is scheduled for next Tuesday, and Assange will remain in custody until then because he was deemed to be a flight risk.
Reuters, The Associated Press and msnbc.com staff contributed to this report.