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Piracy activists have carried out coordinated attacks on websites owned by the music and film industry.

The assault temporarily knocked the Motion Picture Association of America (MPAA) and the Recording Industry Association of America (RIAA) offline.

The attacks were declared on notorious message-board 4chan and were reportedly in retaliation for anti-piracy efforts against file-sharing websites.

The group has declared it will continue to target other sites.

Next in their sights is the British Phonographic Industry (BPI), which it has said will come under attack on 20 September.

"Operation payback", as it is known, is reportedly revenge for the MPAA and RIAA's action against the file-sharing website The Pirate Bay.

Their call to arms was reportedly prompted by a statement by Indian software firm Aiplex, which .

Specifically, the firm said that it used Distributed Denial of Service (DDoS) attacks, where a website is bombarded by requests for pages, effectively taking it offline.

The anonymous activists chose to use the same method to take Aiplex and the other organisations offline.

"We brought them down the same way they brought down The Pirate Bay, with a distributed denial of service," the group said in message posted on the web.

"They hired aiplex.com, who has been taken care of as well. They struck first, we struck harder."

The group has advised members to download software to help flood servers and has reportedly used botnets - networks of computers infected with malicious software and under the control of a hacker or criminal - to flood the websites.

A spokesperson for Aiplex confirmed the action to ´óÏó´«Ã½ News.

"Our site was under attack for some time," he said, adding its site had been taken offline for "about a day and half" over the weekend.

The MPAA has also confirmed the attack and said that it had "taken measures" to mitigate the effects.

All of the targeted sites are currently back online, but a message posted on the web suggests that the BPI will be targeted next.

The BPI did not respond to requests for comment.

Sean-Paul Correll of Panda Security .

"How do you stop the collective man power of an entire internet community? You can seize equipment, hunt down the originators of the attack, but this is a group who has prided themselves in remaining anonymous, and have done so very well through the power of the internet."

A similar anonymous group - also reportedly coordinated through 4chan - temporarily blocked access to key Australian government websites plans in protests against plans to introduce net filters in the country, earlier this year.