MasterCard's website experienced intermittent technical problems Wednesday in what appeared to be the latest cyberattack launched in support of WikiLeaks and its jailed founder, Julian Assange.
The apparent denial-of-service attack occurred a day after the company said that it would join Amazon.com, eBay, PayPal and EveryDNS in stopping the process of forwarding donations or providing computer services to WikiLeaks. MasterCard's decision also came the same day that Assange was arrested in Britain on a Swedish warrant for alleged sex crimes.
A MasterCard spokesman, James Issokson, would not say whether it believed WikiLeaks supporters were involved. The website was inaccessible at times throughout Wednesday.
Issokson said the problems started early morning Eastern time. He said consumers could still use their credit cards for secure transactions.
The troubles at MasterCard occurred on the same day as cyberattacks on websites for Swedish prosecutors, the Swedish lawyer whose clients have accused Assange of sexual crimes, and the Swiss authority that froze Assange's bank account.
On Twitter, a shadowy group of "hactivists" operating under the label "Operation Payback" claimed responsibility for the attack. The group Anonymous -- with a history of similar activity -- invited followers to "grab your weapons" and provided a link to hacking software.
Visa's website also appeared inaccessible Wednesday. The company had stopped processing payments to WikiLeaks, whose supporters claimed responsibility for the outage in their Twitter feeds and elsewhere.
David Perry, the global director of education for Trend Micro, a company that specializes in producing anti-virus software, said Anonymous is "a loose affiliation" that cut its teeth a few years ago with hack attacks against the Church of Scientology.
In early 2008, Anonymous claimed responsibility for a denial-of-service attack on scientology.org and for posting sensitive Scientology documents around the Web.
In an Oct. 30 YouTube posting attributed to the group, a video manifesto proclaims a universal right to free speech and Internet access and claims that Anonymous has "over 9,000" members.
"To threaten to cut people off from the global consciousness as you have is criminal and abhorrent," a computer-generated voice on the video says over ominous scenes of warfare and street riots. "The unjust restrictions you impose on us will meet with disaster and only strengthen our resolve to disobey against your tyranny."
Paul Ferguson, senior threat researcher at Micro Trend, said that with Anonymous, "We're talking about a few hundred people at best." He said the group "seems to pick up the societal flag of the day."
"We see this happening around the world. When students get upset about something, they launch a denial-of-service attack," he said.
It's not surprising that hackers would come out to defend Assange, himself an ex-hacker who shares Anonymous' strong free-speech stance, says security technologist and author Bruce Schneier. "It's kids playing politics," Schneier said. "It feels like hackers doing hacker things to defend a fellow hacker."
Schneier and others point out that thousands of denial-of-service attacks -- which overload a website with perhaps millions of frivolous requests for access -- occur every day.
It's an "easy" attack to launch and it doesn't take an army of hackers to do it, agrees Alan Paller, director of research at SANS, an information security firm.
"There are 30 million infected computers -- and they are sitting in places like university labs -- that can be accessed remotely and harnessed for such an attack," Paller says. "It doesn't take many of them to launch a successful attack."
Patrick O'Shea, a professor at the University of Maryland's Cybersecurity Center, says " 'coordinated' isn't really the right word."
Some experts label public calls on the Internet for others to help bring down a site a "swarm" attack, but O'Shea says it's more accurate to compare it to crowdsourcing -- the online practice of asking a large group of people to help gather information.
Many of the people who respond to Anonymous' call to arms are responding more to the issue at hand than the desire to be part of the hack, O'Shea said.
"It's not just a technology or computer problem," he said. "Now, it becomes a social problem, too."
Material from the Associated Press was used in this report