Spanish police have arrested five people suspected of hacking into or outright disabling thousands of Internet pages, some of them run by government agencies in the U.S., Latin America and Asia, authorities said Saturday.

The National Police said the suspects belonged to one of the most active hacker groups on the Internet and said two of the suspects are 16 years old. The others are 19 or 20.

On the Internet, the group calls itself D.O.M Team, police said.

One of the group's techniques was to infiltrate Web sites and insert a page of its own, police said.

The group attacked some 21,000 Web pages over the last two years, police said in a statement. The five were arrested this week in Barcelona, Burgos, Malaga and Valencia.

The statement did not identify which government Web sites the suspects are accused of tampering with.

The Spanish newspaper El Mundo reported in March that the group had infiltrated NASA's Web page. A police official said Saturday she could not confirm this, and she refused to specify which sites had been hit. The official spoke on condition of anonymity in line with department rules.

The newspaper said the group also hacked the Venezuelan national telephone company's page and that of the Spanish telephone operator Jazztel, among others.

El Mundo said it had contacted the group in March and that members described themselves not as delinquents, but as computer-lovers who raided Web sites to show system administrators the pages' vulnerabilities.

The Spanish investigation began in March after the Web page of a Spanish political party, Izquierda Unida, was disabled shortly after Spain's general election March 9.

The five suspects did not know one another personally, but rather just over the Internet, police said. They were in contact with other members of the hacking group, mainly in Latin America, police said.