The Anonymous hacking network declared war on the Islamic State. The "hacktivist" collective vowed vengeance for attacks in Paris on Friday, claimed by IS, that left 129 dead and hundreds injured, some of them critically.

"Anonymous everywhere in the world is going to hunt you down," a hooded figure in black, wearing the group's signature Guy Fawkes mask said in French in a Youtube video.

"Our country, France, was hit in Paris on November 13 around 2200 (2100 GMT) by multiple terrorist attacks claimed by you, the Islamic State," the figure said in a gravelly, computer-altered voice.

"We are going to launch the biggest operation every mounted against you -- get ready for a multitude of cyberattacks. War has been declared."  The group says it has identified more than 39,000 suspected ISIS profiles and reported them to Twitter. It claims to have had more than 25,000 of these accounts suspended, while nearly 14,000 more on the targeted list remain active.

The nearly three-minute Anonymous clip opens with thundering orchestral music, displaying the Anonymous logo of a suited figure with a question mark for a head.

The video, posted the day after the attacks, had more than 1.3 million views by Monday afternoon.

In an apparent riposte, a message posted on the Twitter address of the messaging service Telegram calls on Islamic State affiliates to secure their Internet communications.

"The #Anonymous hackers threatened... that they will carry out a major hack operation on the Islamic state (idiots)," the message said.

"So U should follow the instructions below to avoid being hacked," it continued, advising followers to avoid opening unknown links and to frequently change computers and phones.

Charlie Winter, a researcher in transnational jihadism at UK-based think tank Quilliam, affirmed the message's authenticity in a tweet.

"@GroupAnon, IS didn't like your declaration of war," he wrote, referring to one of Anonymous' Twitter addresses.

French cybersecurity expert Olivier Laurelli warned the Anonymous action against the jihadist organisation could interfere with police efforts to identify and track its members.

Being able to identify connections and communications between individuals is also critical. But if Anonymous forces accounts to shut down, investigators are left with dead ends.

Besides, the impact is only temporary, he added. "An account closed here, is just another one opened over there," he said.

Anonymous also retweeted a link to the following message from the hacktivist group Binary Sec:

“We as a collective will bring an end to your reign of terror. We will no longer turn a blind eye to your cruel and inhumane acts of terrorism towards all other religions that are not Islam. We’ve watched you behead innocent people, kidnap and murder children, and then launch terrorist attacks in France. This will NOT BE TOLERATED ANY LONGER. We here at BinarySec live for the sole purpose of bringing down All ISIS Propaganda ONE website and/or person at a time. ISIS… Your Jihad is coming to an abrupt end . We here at BinarySec will be one of the driving forces to your end and that’s a promise. ISIS… The War Is On.”

This is not the first time that Anonymous has taken on ISIS. Foreign Policy Magazine reports that the conflict between hackers that identify with Anonymous and ISIS has waged online for more than a year. A tipping point that forced many hackers to join the cause were the attacks on the Charlie Hebdo newspaper and kosher market in Paris earlier this year.

According to the FP report from last week, hackers have taken 149 Islamic State-linked websites offline and flagged roughly 101,000 Twitter accounts and 5,900 propaganda videos.

The remaining question is whether or not these hackers aiming to achieve social good are helping or harming state-driven attempts to take out the terror group. Technology companies have said in the past that government intelligence agencies ask them not to take down ISIS-related content because, when using the legal avenues at hand, they are able to more effectively track these groups.

Anonymous is an international network of activist computer hackers which has claimed responsibility for many cyberattacks against government, corporate and religious websites over the past dozen years.

Since the attack on French weekly Charlie Hebdo last January, which led to the deaths of 17 victims, Anonymous activists have waged an online vigilante campaign to force the shutdown of Twitter profiles suspected of belonging to ISIS supporters.