The global hacking collective has declared war on ISIS, following last week's attacks in Paris.
In a video posted in French on YouTube, a representative wearing the group’s distinctive Guy Fawkes mask said the violence "would not go unpunished".
"You, the vermin who kill innocent victims, we will hunt you down like we did to those who carried out the attacks on Charlie Hebdo.
“So get ready for a massive reaction from Anonymous. Know that we will find you and we will never let up."
A video was also released in English in which a "total mobilisation" was promised.
"We're tracking down members of the terrorist group responsible for these attacks, we will not give up."
Anonymous is a decentralised hacking group that is known for its cyber-attacks on governments and organisations.
Earlier this month it leaked a list of 350 names it claimed were Ku Klux Klan members, having already hijacked the group's Twitter account.
The latest video ends with the group's standard mantra: "We are anonymous. We are legion. We do not forgive. We do not forget. Expect us."