The website of credit card giant Visa was knocked offline on Wednesday by supporters of WikiLeaks, who also took aim at US conservative standard bearer Sarah Palin and US Senator Joe Lieberman. went down instantaneously at 4:00 pm (2100 GMT) as members of the hackers group known as "Anonymous" launched a coordinated cyber attack on the site.

"Operation Payback. TARGET: WWW.VISA.COM :: FIRE FIRE FIRE!!! WEAPONS," Anonymous announced on their Twitter feed @Anon_Operation.

Two hours after the attack the remained inaccessible. So was the site attacked earlier in the day for cutting off payments to WikiLeaks.

Members of Anonymous, in an online chat with AFP, vowed to attack anyone with an "anti-WikiLeaks agenda" and they extended their cyber assaults on Wednesday to the websites of Palin and Lieberman.

Palin has described WikiLeaks founder Julian Assange as "an anti-American operative with blood on his hands" and asked "Why was he not pursued with the same urgency we pursue al-Qaeda and Taliban leaders?"

Her website,, came under cyber attack from a "small group of Anonymous protestors," according to Sean-Paul Carroll, a threat researcher at PandaLabs, the malware detection laboratory of Panda Security.

Carroll said the Palin website went down for about six minutes.

According to ABC News, besides attacking the Palin website, the hackers also "disrupted" the personal credit card accounts of Palin and her husband, Todd.

"No wonder others are keeping silent about Assange's antics," ABC News quoted Palin as saying in an email.

"This is what happens when you exercise the First Amendment and speak against his sick, un-American espionage efforts."

Carroll said Anonymous members also briefly took down the website of Senator Lieberman, who issued an early call for US companies to withdraw their technical support from WikiLeaks, an appeal which has been widely followed.

In addition to Visa and Mastercard, Anonymous has already taken credit for temporarily taking down the websites of PayPal, the Swiss Post Office bank and others with distributed denial of service (DDoS) attacks.

In a typical DDoS attack, computers are commanded to simultaneously visit a website, overwhelming its servers, slowing service or knocking it offline completely.