Hacking group Anonymous has posted a video warning terrorists belonging to the so-called Islamic State militant group that they will "hunt them down."
Speaking in French from behind the signature Guy Fawkes mask, a spokesman said: "War is declared."
The hackers will use their skills to bring down the militants, he said, in what he vowed would be "the biggest operation ever".
The group has been targeting the social media accounts of suspected extremists or Islamic State supporters since January's attack on French satirical magazine Charlie Hebdo
This includes posting the details of hundreds of Twitter accounts potentially involved in spreading radical propaganda.
Yesterday the group posted a list containing more than 1,000 account details to a text-sharing site, with the message: "ISIS Supporters and Militants. We Are Anonymous. We Do Not Forgive. We Do Not Forget. Expect us!"