The websites of the international credit card MasterCard and the Swedish prosecution authority are among the latest to be taken offline in the escalating technological battle over WikiLeaks, web censorship and perceived political pressure.
Co-ordinated attacks by online activists who support the site and its founder Julian Assange – who is in UK custody accused of raping two Swedish women – have seen the websites of the alleged victims' Swedish lawyer disabled, while commercial and political targets have also been subject to attack by a loose coalition of global hackers.
The Swedish prosecution authority has confirmed its website was attacked last night and this morning. MasterCard was partially paralysed today in revenge for the payment network's decision to cease taking donations to WikiLeaks.
In an attack referred to as Operation Payback, a group of online activists calling themselves Anonymous appear to have orchestrated a DDoS (distributed denial of service) attack on the financial site, bringing its service to a halt.
Attempts to access www.mastercard.com have been unsuccessful since shortly after 9.30am.
The site would say only that it was "experiencing heavy traffic on its external corporate website" but insisted this would not interfere with its ability to process transactions.
But one payment service company told the BBC its customers were experiencing "a complete loss of service" on MasterCard SecureCode. The credit card company later confirmed that loss.
Meanwhile it has also emerged that Visa has today ordered DataCell, an IT firm that helps WikiLeaks collect payments, to suspend all of its transactions – even those involving other payees – a day after it cut off all the firm's donations being made to WikiLeaks.
DataCell, a small Icelandic company that facilitates transfers made by credit cards including Visa and MasterCard, says it will take up "immediate legal actions" and warned that the powerful "duopoly" of Visa and MasterCard could spell "the end of the credit card business worldwide".
Andreas Fink, chief executive of DataCell, said in a statement: "Putting all payments on hold for seven days or more is one thing but rejecting all further attempts to donate is making the donations impossible.
"This does clearly create massive financial losses to WikiLeaks, which seems to be the only purpose of this suspension.
"This is not about the brand of Visa; this is about politics, and Visa should not be involved in this.
"Visa customers are contacting us in masses to confirm that they really donate and they are not happy about Visa rejecting them. It is obvious that Visa is under political pressure to close us down."