The attacks stepped up Wednesday, a day after Mr. Assange was arrested and denied bail in London in connection with sexual-misconduct accusations in Sweden. A range of organizations, including MasterCard Inc., and the Swedish prosecutor's office, reported technical difficulties with their websites that appear to stem from so-called denial of service attacks, in which computers flood a server to prevent it from displaying a Web page.
The attacks have hit eBay Inc.'s PayPal and Swiss bank PostFinance.
PayPal refused to handle payments to WikiLeaks and PostFinance closed Mr. Assange's account.
Although these attacks caused some business disruption, they were mostly annoying rather than crippling.
The computers in the office of Claes Borgstrom, the lawyer representing the two women making the accusations against Mr. Assange, also crashed.