The hacking group Anonymous appears to have declared war on the Islamic State in Iraq and Syria (ISIS) in the wake of Friday’s devastating terror attacks on Paris.

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In an unverified video posted to YouTube on Saturday, a spokesperson wearing the group’s signature Guy Fawkes mask warned the group that “war is declared” and to expect “major cyberattacks.”

"Anonymous from all over the world will hunt you down. You should know that we will find you and we will not let you go. We will launch the biggest operation ever against you," the spokesperson said in French.

ISIS on Saturday claimed responsibility for the deadly attacks that killed 129.

Anonymous made similar threats following the attacks on the satirical French newspaper Charlie Hebdo in January. The group in February posted hundreds of social media accounts and websites that it claimed were affiliated with the jihadist group.

The hacking collective launched a series of denial-of-service attacks on ISIS sites, flooding the pages with phony traffic to disable them. Many of the Twitter accounts the group outed were ultimately suspended.

Intelligence officials use ISIS’s prominent online presence to track its activities, and some suspect U.S. spies have created fake jihadist websites to attract its members.

This led some foreign policy experts to criticize the Anonymous campaign on the grounds that it could hurt intelligence gathering.

Others questioned the effectiveness of the hacks, because ISIS can easily revive Web activities under new accounts.

Anonymous — a loosely affiliated collective — has come under fire in the past for leaking inaccurate information and failing to control its members.

While the group gained early support for its campaigns targeting the Church of Scientology and the Westboro Baptist Church, it later faced criticism for incorrectly identifying the shooter of Michael Brown in Ferguson, Mo.

Anonymous remains a polarizing group. It appears to be firmly on the side of the U.S. when it comes to the conflict with ISIS, but skeptics question both its motives and abilities.

“The motivation of Anonymous as a whole really is to get attention,” Matt Harrigan, president and CEO of cyber threat detection firm PacketSled, who monitors the hacking group, told The Hill this month. “It's a PR machine for causes that somebody inside Anonymous has decided are important.”

The group earlier this month released a much-anticipated list of around 375 alleged Ku Klux Klan members who appeared to be largely culled from public data and fell far short of a promise to “unmask” 1,000 KKK members.

Saturday’s message was not posted to the group’s official YouTube channel, but a tweet from the official Anonymous account said that the group was at war with Daesh, another name for ISIS.