The file-sharing website Megaupload.com has been taken down by US officials after the site's founders were charged with violating copyright laws.
US prosecutors have said the copyright holders have accrued costs of $175 million in criminal proceeds and more than $500m in copyright damages.
In a statement, the US justice department said that it was "one of the largest criminal copyright cases ever brought by the US" and that the website represents an "international organised criminal enterprise allegedly responsible for massive worldwide online piracy of numerous types of copyrighted works".
In a further development, Anonymous hackers have claimed on social networking site Twitter that they are responsible for attacks on US government sites and copyright holders as part of a campaign to retaliate over the Megaupload shut down.
On the @AnonymousWiki Twitter account it read: "We Anonymous are launching our largest attack ever on government and music industry sites. Lulz. The FBI didn't think they would get away with this did they? They should have expected us."
US government sites such as the Department of Justice and FBI along with rights holders Universal Music have had their websites attacked by a swarm of internet traffic owing to web links that allow a user's computer to take part in the attack when clicked without the user realising.
At the time of writing, Universal Music's website says "The Site is under maintenance. Please expect it to be back shortly".
IT security firm Sophos has warned users that by clicking on an Anonymous link, users could be carrying out a distributed denial of service (DDoS) attack on the US government.
Graham Cluley, senior technology consultant at Sophos emphasized that DDoS attacks are illegal and that those who participate voluntarily or mistakenly in clicking Anonymous links risk being prosecuted.
"I'm not sure if participants in this instance would get away with claiming that they innocently clicked on links by mistake, so make sure you always trust the links you click on, even if they're shared by a friend on social networking sites," he said.