'Anonymous' Hackers hit Mastercard and Visa over Wikileaks row

The attacks came after hackers pledged to pursue firms that have withdrawn services from Wikileaks.

Despite MasterCard payments being disrupted, the firm however said there was "no impact" on people's ability to use their cards. Visa's website also experienced problems - the attacks came after both companies stopped processing payments to the whistle-blowing site.

Mastercard admitted there had been "a service disruption" involving its SecureCode system, but it added: "Our core processing capabilities have not been compromised and cardholder account data has not been placed at risk.

"While we have seen limited interruption in some web-based services, cardholders can continue to use their cards for secure transactions globally."

Entries on the Twitter page of Operation Payback, the Anonymous campaign, announced the Visa site had been taken down. However, Visa's website was later restored and a spokesperson affirmed that its processing network, which handles cardholder transactions, was working normally.

But in a day of fast-moving developments, the Anonymous Twitter page then went down, replaced by a message from Twitter saying the account had been suspended and refusing to comment on “the actions we take on specific user accounts".

However, the BBC reported that, according to sources, that the last tweet sent out by Anonymous included a link to a file containing consumer credit card information.