GCHQ, the British signals intelligence service, is in the dock accused of hacking computers without individual warrants in order to tap communications.
The allegations, made by messaging providers and campaign groups GreenNet, RiseUp Networks, Chaos Computer Club and Privacy International, among others, concern the use by the U.K. Government Communications Headquarters of "thematic warrants" to hack computers. They began making their cases to the U.K.'s Investigatory Powers Tribunal in London on Tuesday, in hearings scheduled to run through Friday.
GCHQ first admitted to hacking in February following Privacy International's initial legal challenge.
Documents released by the court on Tuesday confirm that GCHQ hacks computers without individual warrants, according to Privacy International, which published the documents on its website.
The campaign groups were not the only ones concerned about the extent and lawfulness of GCHQ's activities: The U.K.'s Commissioner of the Intelligence Services investigated in 2014, eventually publishing a report in July this year expressing concerns that the warrants relied on by GCHQ were too broad.
The court documents show that U.K. Secretary of State does not individually approve hacking operations outside the U.K. unless they involve "additional sensitivity" or "political risk," Privacy International said.
Furthermore, when there are explicit authorizations, they do not identify or describe the equipment to be hacked, or even name the equipment users to be spied on, it said.
The full extent of the U.K. intelligence services' hacking activities will never be known as the Security Service (MI5) and the Secret Intelligence Service (MI6) failed to keep accurate records, a matter the government's own Intelligence and Security Committee found "unacceptable" in a March 2015 report included among the court documents.
Calling the authorities to account now will not necessarily improve things in the future. Earlier this month, the U.K. government presented a draft law, the Investigatory Powers Bill, which if approved without amendment will give the intelligence services freedom to hack almost anyone.