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As France intensifies its air raids against Islamic State, a separate front has opened against the fundamentalist group: cyber warfare.

Hacking collective Anonymous accessed and took down more than 5,500 social media accounts associated with Islamic State, it said on Twitter. Following the Paris terrorist attacks on Friday, the activist hackers declared “war” against Islamic State, threatening to track down the group’s members.

“You should expect a massive reaction from Anonymous, you should know that we will find you and we won’t let go,” Anonymous said of Islamic State in a video posted online on Saturday. “We are going to launch the biggest operation ever against you. Expect numerous cyberattacks. The war is on. Get ready.”

The push by Anonymous came as France started a wave of aerial strikes on the Islamic State stronghold of Raqqa after the attacks in the French capital, in which at least 129 people died. Anonymous’s rhetoric echoed that of French Prime Minister Manuel Valls, who said in a Monday radio interview “We will act on all fronts to destroy Islamic State.”

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Anonymous, a loose association of hacking activists, started a similar offensive against Islamic State after the murderous attacks on Charlie Hebdo and a Jewish delicatessen in Paris in January, shutting down hundreds of social media profiles. Activists involved in the latest Anonymous campaign, dubbed #OpParis, said Monday on Twitter that they had closed down thousands of Islamic State profiles on the social network.

As part of its efforts, Anonymous published a guide for supporters of how to identify and clean out Islamic State-linked accounts. The hacker group is also spamming social-media threads linked to Islamic State with rick-rolling, an online prank where a video of the 1987 song “Never Gonna Give You Up” by British singer Rick Astley is posted.

The fundamentalist group responded by publishing a guide for its members on how to hide their online presence, for example by concealing your Internet protocol address. A side effect of the online battle is that it makes identifying extremists more difficult for security forces, according to one cybersecurity expert.

“It’s a bit like stepping all over a crime scene," said Loic Guezo, a Paris-based cybersecurity strategist at IT security company Trend Micro Inc. “Police may be surveilling a suspected jihadi Twitter account and lose track because Anonymous intervened, albeit with the best intentions."