Hackers have once again disabled the Web site of the Recording Industry Association of America, a group of record labels that is leading the charge in the crackdown on online music piracy.

The attack, which began Friday, has caused the site to be unavailable for three days, an RIAA representative confirmed Monday. It follows several other malicious attacks on the site last summer.

"How pathetic that those who want free music don't believe in free speech," RIAA spokeswoman Amy Weiss said in a statement. "We will continue to fight theft on the Internet and work hard to make sure that songwriters, artists and other copyright holders continue to get paid for their work."

The trade association, along with the Motion Picture Association of America (MPAA), has won many critics in its quest to shut down popular file-trading networks such as Napster and Kazaa. Big music labels blame online piracy for a dramatic drop in music CD sales.

In the battle to deter illegal online file swapping, the RIAA won a critical round last week when a federal judge, invoking the 1998 Digital Millennium Copyright Act, ordered Internet service provider (ISP) Verizon Communications to disclose the identity of an alleged Internet music pirate.

Verizon plans to appeal the decision. If upheld, the ruling would set a legal precedent, giving music industry investigators the power to subpoena ISPs for the names of hundreds or thousands of subscribers suspected of music piracy at a time, without having to obtain a judge's approval first. Many consumer and privacy groups, as well as ISPs, opposed the decision.

An RIAA representative declined to speculate on who was behind the attack or the reasons for it.

The group's site appeared to have been seized by a denial-of-service attack, the same type of problem that brought down the site in July.

Denial-of-service attacks overwhelm an Internet site by enlisting hundreds or thousands of other machines in a mass attempt to make simultaneous connections to the site. The resulting overload resembles a physical traffic jam: Few people can get through.

The RIAA is working to restore the Web site, and the FBI and United States Secret Service are investigating the attacks, according to Weiss. Such attacks are illegal under federal and state laws and carry penalties of up to five years in prison.