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By Holly Ellyatt, CNBC

Activist hacking group Anonymous and their followers are carrying out a "trolling day" against the terrorist group ISIS as part of its cyber-campaign against the militant Islamist group.

In an online message posted this week, Anonymous asked people to troll ISIS, or "Daesh" as it is also known in the West (a derogatory term for the group), online as part of its "Operation ISIS" campaign.

Trolling is the term given to abuse, insults or threats made online with celebrities often being the targets of internet "trolls." Many ISIS supporters and members have social media accounts and the jihadist group as a whole has a sophisticated online presence.

Read More from CNBC: Anonymous Declares This Friday 'ISIS Trolling Day'

Anonymous claims it has already taken down hundreds of Facebook and Twitter accounts belonging to ISIS but wanted people to join in a mass trolling event.

The activist group, who have previously hacked corporations and governments, declared cyber "war" on ISIS after the Nov. 13 attacks in Paris in which 130 people died.

Earlier in the week, Anonymous had asked people to mock ISIS, posting a message online that read:

"We ask you to show your support and help against ISIS by joining us and trolling them // do not think you have to be part of Anonymous, anyone can do this and does not require special skills."

"We ask you to take part of this on Facebook // Twitter // Instagram // Youtube //In the 'Real World,'" the post on file-sharing website Ghostbin added.

Read More from CNBC: What Can Anonymous Really Do to ISIS?