A protester seen during a demonstration by supporters of the Anonymous movement, as part of the global "Million Mask March" protests in Nantes in 2014. REUTERS/Stephane Mahe Anonymous has begun leaking the personal information of suspected extremists after it "declared war" on ISIS following the deadly attacks in Paris.

The activist collective is assembling lists of the Twitter accounts and websites of extremists, in an attempt to have them taken down. At least one post seen by The Independent contains details including the physical address of a person it says is an ISIS recruiter in Europe.

Activists claim to have successfully had accounts and sites taken down already.

The group appears to have stepped up its tactics for what it called its "biggest operation" ever, in response to the attacks that left 129 dead. Previously it had largely focused on social-media accounts.

None of the details that have been shared could be independently confirmed, and Anonymous activists have misidentified extremists in the past. But if true the details shared include the physical addresses and names of those the activists claim are involve in recruitment.

Anonymous began its campaign against ISIS in earnest after the killings at Charlie Hebdo in January. That work included launching attacks on extremist websites and finding extremist accounts on Twitter so the social network could take them down.

It has continued that work this time around. Its attacks on websites seem to use a distributed denial of service, a technique that overloads a site's servers until they go offline. The Twitter accounts are taken down by the network itself, in response to requests the activists make once they are found.