Zurich - An anonymous group of hackers said on Wednesday they had launched online attacks to shut down the websites of credit card Mastercard and a Swiss bank that cut off business ties with WikiLeaks.
The self-styled 'hacktivist' group dubbed Anon_Operation said in one tweet that "www.mastercard.com/ is down" and the site of the credit card giant could not be accessed from Geneva.
On their homepage the group, which claims it is fighting for "freedom on the internet" and against censorship designated mastercard.com as their "current target" in what was taking the proportions of cyber war.
It quoted John Perry Barlow, co-founder of the San Francisco-based internet freedoms group Electronic Frontier Foundation, as saying on microblogging service Twitter: "The first serious infowar is now engaged. The field of battle is WikiLeaks. You are the troops."
The Swiss post office banking service, PostFinance, confirmed on Wednesday that its website was suffering denial of service attacks since it closed the bank account of WikiLeaks founder Julian Assange on Monday.
"Since the closure of the account, groups have launched 'Operation Payback' with the aim of blocking PostFinance by simulating hundreds of thousands of connections with the aim of overloading it," said PostFinance spokesperson Alex Josty.
The spokesperson said the hackers had not endangered its payment systems or account managements.
"The situation improved on Wednesday but the attacks are continuing," the spokesperson added.
Grab your weapon
Attempts to connect to the Postfinance.ch website earlier on Wednesday produced error messages but it later came back online with notices warning of disruption.
"Target: postfinance.ch : Grab your weapon and its settings: FIRE NOW!" said one tweet on Anon_Operation.
PostFinance closed an account set up by Assange because he gave "false information" on his address, claiming he lived in the Swiss city of Geneva, in violation of banking and money laundering rules.
The bank insists that any deposit belongs to Assange and the money can be transferred where he wishes.
News website CNET cited a MasterCard spokesperson as saying the whistleblowing website was being cut off due to rules barring use for "directly or indirectly engaging in or facilitating any action that is illegal".
Visa followed its credit card rival in suspending all payments to WikiLeaks, a spokesperson for the debit card company said on Tuesday.
US-based online payment service PayPal has also blocked financial transfers to WikiLeaks after governments around the world sought legal action against the site following its publication of sensitive US diplomatic cables.
The whistleblowing site says it has also come under attack, including during the weekend when a hacker disabled the website according to internet security firm Panda Labs.
A statement purportedly issued by the hacker, or hackers, at Twitter claimed the assault was retaliation for WikiLeaks "attempting to endanger the lives of our troops, other assets and foreign relations," according to Panda.
Assange was denied bail in London on Tuesday after his arrest on a warrant from Swedish police on suspicion of rape offences.