Megaupload, one of the internet's largest file-sharing sites, has been shut down by officials in the United States.
The site's founders have been charged with violating piracy laws. The news came a day after anti-piracy law protests, but investigators said they were ordered two weeks ago.
Federal prosecutors have accused Megaupload of costing copyright holders more than $US500 million in lost revenue. The company says it was diligent in responding to complaints about pirated material.
In response, hackers group Anonymous has targeted the FBI and US Department of Justice websites, the BBC reports.
The FBI website was intermittently unavailable due to what officials say is being treated as a malicious act.
The Motion Picture Association of America's website has also suffered disruption.
Megaupload's co-founders Kim Dotcom, formerly known as Kim Schmitz, and Mathias Ortmann were arrested in Auckland, New Zealand on Friday along with two other employees of the business at the request of US officials.
Two corporations and three other men have been arrested overseas.
All seven men are charged with running an international organised criminal enterprise, allegedly responsible for worldwide online piracy of numerous types of copyrighted works including books, music and movies. They face up to 20 years' jail, if convicted.
The BBC reports the case adds to the debate over online piracy in the United States as a controversial proposed bill - the Stop Online Piracy Act (Sopa) - suggests greater powers are needed for authorities to tackle copyright theft.