In the clip, a figure wearing the group's symbolic Guy Fawkes mask is seated in front of a desk with the hashtag #OpCharlieHebdo - which stands for Operation Charlie Hebdo - featured on screen.
The figure, whose voice is obscured says: "We are declaring war against you, the terrorists."
They add that the group will track down and close all accounts on social networks related to terrorists in order to avenge those who have been killed.
This is backed up with a statement entitled "a message to the enemies of freedom of expression" posted to Pastebin, the hacker collective offered their condolences to "the families of the victims of this cowardly and despicable act".
They write "freedom of expression has suffered inhuman assault ... and it is our duty to react".
Anonymous are a group comprised of activists and hackers who claim to defend and protect democracy.
Video on Telegraph UK.
But this isn't the first time they've targeted terrorists, though. Last year they threatened ISIS with #OpIceISIS, and they're stronger than ever.
Good luck to them.