The Anonymous hackers collective has announced that it's preparing to unleash waves of cyber attacks on the Islamic State (IS) following the attacks in Paris last week that killed more than 130 people, it said in a video posted online.

A man wearing a Guy Fawkes mask said the IS militants who claimed responsibility for the Paris attacks were "vermin" and Anonymous would hunt them down.

"These attacks cannot remain unpunished," the man said in the video, speaking in French.

"We are going to launch the biggest operation ever against you. Expect many cyber attacks. War has been declared. Get ready," the man said, without giving details of what the attacks would involve. "We don't forgive and we don't forget."

Anonymous is an international network of activist computer hackers which has claimed responsibility for many cyber attacks.

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