The new boss of GCHQ, Robert Hannigan, has warned that social networking sites have become central to terrorist groups and tech giants need to work more closely with spy agencies to address this.
In an article in the Financial Times, Hannigan said however much the tech companies may dislike it, "they have become the command and control networks of choice for terrorists and criminals, who find their services as transformational as the rest of us."
While not singling out Facebook or Twitter, Hannigan said social media sites are used by terrorists to disseminate propaganda and communicate with other members and the wider world.
YouTube was used to show beheadings of journalists and aid workers. These videos were quickly spread on Twitter.
Hannigan said freely available technology has helped terror groups hide from the security services and said major tech firms were "in denial" about this. He added that smartphones and tablets had "increased the options available exponentially" to conceal terrorist activity.
Furthermore, privacy is not an "absolute right", he continued, and GCHQ has to enter the debate over it.
"GCHQ is happy to be part of a mature debate on privacy in the digital age. But privacy has never been an absolute right and the debate about this should not become a reason for postponing urgent and difficult decisions," he said.
"I think we have a good story to tell. We need to show how we are accountable for the data we use to protect people, just as the private sector is increasingly under pressure to show how it filters and sells its customers' data."
Eric King, deputy director of Privacy International, told the Guardian that it was "disappointing to see GCHQ's new director refer to the internet the greatest tool for innovation, access to education and communication humankind has ever known as a command-and-control network for terrorists."
King added that GCHQ had lost the trust of the public and does need to enter a public debate over privacy "but attacking the internet isn't the right way to do it."
