After WikiLeaks appealed for donations so that it could continue publishing confidential US diplomatic cables, Mastercard and Visa said they were suspending payment to the site.
Hackers hit back on Thursday. Declaring that it is fighting for “freedom on the internet”, a group calling itself AnonïOperation said they had brought down www.mastercard.com.
The company has declined to comment.
Swiss post office banking service PostFinance confirmed Wednesday that its website was suffering “denial of service attacks” since it closed Assange’s bank account on Monday.
The site seemed to be functioning by mid-afternoon.
Assange’s son Daniel, a software developer in Australia who has not been in contact with his father for several years, called for the WikiLeaks founder to be treated “fairly and apolitically”, as suspicion grows that a Swedish arrest warrant for Assange Senior is a step towards extradition to the US.
Claes Borgstroem, the lawyer for the two women who have lodged accusations of rape, on Wednesday insisted that there is “absolutely no link” between their charges and “the CIA or the American administration”, which is furious over the leaks.
High-profile British human rights lawyer Geoffrey Robertson is to defend Assange in his attempt to avoid extradition to Sweden.
He will return to court on 14 December.
The US government announced on Tuesday that it will organise International Press Freedom Day in Washington next May in an effort to protect "the free flow of information".
"New media has empowered citizens around the world to report on their circumstances, express opinions on world events, and exchange information in environments sometimes hostile to such exercises of individuals' right to freedom of expression," said State Department spokesperson Philip Crowley.
"At the same time, we are concerned about the determination of some governments to censor and silence individuals, and to restrict the free flow of information."
Among WikiLeaks’ latest revelations are:
Spain’s Socialist government offered to host the US’s Africa military command, Africom, at the US naval base of Rota, near the southern port of Cadiz.
Libya threatened the UK with “dire consequences” if alleged Lockerbie bomber Abdelhasat Ali Mohamet al-Megrahi, who was suffering from cancer, died in a Scottish prison. That led Britain’s ambassador to Tripoli, Sir Vincent Fean, to say that his country’s business interests would be "cut off at the knees" if he was not freed.
Saudi Arabia has a lively and illegal party scene run by members of the royal family. Locally made moonshine is drunk, in breach of the kingdom’s anti-alcohol law, prostitutes are hired and drugs consumed.
Tunisia has blocked the website of Lebanese newspaper al-Akhbar after it published WikiLeaks cables saying that President Zine el Abidine Ben Ali’s wife and her family are deeply unpopular and that his regime is corrupt and repressive.