The 'tarrant effect': what impact did far-right attacks have on the 8chan forum?

This paper analyses the impact of a series of mass shootings committed in 2018-2019 by right-wing extremists on 8chan/pol, a prominent far-right online forum. Using computational methods, it offers a detailed examination of how attacks trigger shifts in both forum activity and content. We find that while each shooting is discussed by forum participants, their respective impact varies considerably. We highlight, in particular, a 'Tarrant effect': the considerable effect Brenton Tarrant's attack of two mosques in Christchurch, New Zealand, had on the forum. Considering the rise in far-right terrorism and the growing and diversifying online far-right ecosystem, such interactive offline-online effects warrant the attention of scholars and security professionals.