In recent months, 8chan has become a go-to resource for violent extremists. At least three mass shootings this year have been announced in advance on the site, often accompanied by racist writings that seem engineered to go viral on the internet.
Earlier this month, Crown Prince Mohammed told CBS in an interview that Saudi schools have been "invaded" by elements of the Muslim Brotherhood, which has been designated by Saudi Arabia as a terrorist organisation along with other militant groups such as al Qaeda and Islamic State.
In the wake of Britain's third major attack in three months, PM Theresa May called on governments to form international agreements to prevent the spread of extremism online. Here's a look at extremism on the web, what's being done to stop it and what could come next.