PURCHASE, N.Y. (AP) — The website for MasterCard suffered severe technical problems Wednesday, possibly the result of attacks by hackers supporting WikiLeaks founder Julian Assange. Credit cards were not affected.

Supporters of the organization, which has released thousands of classified government documents in recent weeks, said they would attack companies and groups hostile to its founder. An Internet group operating under the label “Operation Payback” claimed responsibility for the MasterCard problems in a message on Twitter. The hacking group Anonymous is distributing software tools that allow anyone with a computer and an Internet connection to join in the attacks.

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MasterCard spokesman James Issokson would not say whether it believed WikiLeaks supporters were involved. The website was inaccessible as of late Wednesday morning. Issokson said the problems started early morning Eastern time.

Consumers can use MasterCard’s website to find information about its credit cards, but applying for one and accessing existing accounts are done through the banks that issue the cards.

MasterCard Inc. pulled the plug on its relationship with WikiLeaks on Tuesday, the latest in a string of U.S.-based companies — Amazon.com Inc., eBay Inc.’s PayPal and EveryDNS — to do so amid intense government pressure. The actions of MasterCard and others have hurt WikiLeaks’ ability to raise money.

MasterCard’s troubles occurred on the same day of attacks 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.

MasterCard was trying to restore service Wednesday, but Issokson could not say how long it would take. Issokson said the website’s technical problems have no impact on the ability of consumers to use credit cards for secure transactions.

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In a statement, MasterCard said its systems have not been compromised.

“At this time the issue appears to be the result of a concentrated effort to flood our corporate web site with traffic and slow access. We are working to restore normal service levels,” the company said.

Such an attack, known as a denial of service, is analogous to thousands of people all calling the same phone number at once, resulting in busy signals for the few who are trying to legitimately get through.

The website for Visa appeared to be working normally late Wednesday morning and the company said it was not experiencing any problems.

A British judge sent Assange to jail on Tuesday, denying bail after he vowed to fight efforts to be extradited to Sweden in a sex-crimes investigation.

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