After ISIS claimed responsibility for the Paris attacks, hacktivist group Anonymous then declared "war" on the extremist group.

In the video posted on YouTube, the man wearing the infamous Anonymous mask promised to "launch the biggest operation ever" against ISIS through "cyber attacks."

As a response to the Anonymous announcement, the terrorist group called them "idiots," as per The Hacker News.

But it seems as though Anonymous has the last laugh after successfully hacking the social media accounts of thousands of ISIS militants in #OpParis or Operation Paris. Teen Vogue reports:

"Today [November 17], the hacktivist group made good on its treat and created 'a sophisticated system for detecting and downing ISIS members' Twitter accounts,' reports the New Republic. Supposedly, 3,800-5,500 active ISIS accounts were affected."

Undoubtedly, the Anonymous move helps take down ISIS to an extent - the extremist group uses social media to spread message of hatred, promulgate their propaganda, and recruit new members.

However, it also has its downside: law enforcement agencies use ISIS social media activity to track and monitor their activities; without these, government agencies are crippled in discovering any further attacks that could be avoided.

In Anonymous' press release for #OpISIS or Operation ISIS, the group lists four key players that aim to help take ISIS down: Ghost Security Group, AnonOps IRC, WikiLeaks, and YourAnonNews.

Not only that, but Anonymous is also using a "Distributed Denial of Service" or DDoS attacks to close down websites that are in any way linked to ISIS, including fundraising websites.

And for anyone who wants to get involved and help Anonymous fight off the ISIS online presence, the collective has also released detailed guides. A member of the group wrote:

"Instead of sitting idle in the [chat] channel or lurking around and doing nothing, you can benefit greatly from the different tools and guides that have been provided to you. Your contribution means a lot and we encourage you to partake in all of the Op's activities if you can, the more the merrier."

There are three hacking guides provided by the group: the NoobGuide to hack websites connected with ISIS, Reporter, to set up a Twitter bot to find ISIS accounts, and Searcher to identify and take down ISIS-linked websites and social media accounts.