The online group Anonymous said Wednesday that it had paralyzed the Egyptian government’s Web sites in support of the antigovernment protests.

Anonymous, a loosely defined group of hackers from all over the world, gathered about 500 supporters in online forums and used software tools to bring down the sites of the Ministry of Information and President Hosni Mubarak’s National Democratic Party, said Gregg Housh, a member of the group who disavows any illegal activity himself. The sites were unavailable Wednesday afternoon.

The attacks, Mr. Housh said, are part of a wider campaign that Anonymous has mounted in support of the antigovernment protests that have roiled the Arab world. Last month, the group shut down the Web sites of the Tunisian government and stock exchange in support of the uprising that forced the country’s dictator, Zine el-Abidine Ben Ali, to flee.

Mr. Housh said that the group had used its technical knowledge to help protesters in Egypt defy a government shutdown of the Internet that began last week. “We want freedom,” he said of the group’s motivation. “It’s as simple as that. We’re sick of oppressive governments encroaching on people.”