Anonymous, a hacktivist collective known for its penchant for Guy Fawkes masks and mystery, declared war with Daesh (another name for ISIS) following Friday's attacks in Paris.
A tweet from the group urged followers to “make no mistake” about its stance on the Islamic State.
Using #OpParis, Anonymous posted videos in English, Italian and several other languages claiming the group would “not give up” until it was able to “neutralize” the threat.
Early Monday, Anonymous claimed it vanquished nearly 4,000 pro-ISIS Twitter accounts.
The mysterious nature of Anonymous, however, makes it impossible to verify the group's success.