Hackers claim MasterCard site crash
Hackers claimed to have crashed websites on Wednesday, including MasterCard and Visa in revenge for the firms' withdrawal of support from whistle-blowing site WikiLeaks.
The group of hackers, known as Anonymous, launched the Operation Payback campaign in response to mass suspension of services to the WikiLeaks website after its release of confidential US embassy cables.
Anonymous, understood to be a loose-knit group of internet activists, tweeted: "Target: www.visa.com. Fire fire fire! Weapons!" and "It's down! Keep firing!"
Earlier in the day the group wrote: "We are glad to tell you that www.mastercard.com is down and it's confirmed."
Another message read: "There are some things WikiLeaks can't do. For everything else, there's Operation Payback."
A spokeswoman for Visa said the site was "experiencing heavier than normal traffic" and repeated attempts to load the Visa.com and Visa.co.uk sites were met without success.
So-called distributed denial-of-service (DDoS) attacks also appeared to have been launched against MasterCard, PayPal, PostFinance and the Swedish prosecutors office, which is acting in the legal case against WikiLeaks founder Julian Assange.
The attacks began on Monday, when the PayPal website crashed after hackers made it a target.
John Mueller, PayPal's General Counsel, said the attacks did not affect PayPal's stance on WikiLeaks, whose account would "remain restricted".
A spokeswoman for MasterCard, whose website is now back online but remains slow to load, said that cardholders' payments were "secure" despite hackers' efforts.