SAN FRANCISCO (AFP) - A US judge has ordered the FBI to stop its “pervasive” use of National Security letters to secretly snoop on phone and email records, ruling Friday that the heavily used tactic was unconstitutional. The order issued by US District Court Judge Susan Illston in San Francisco came as a surprising blow to a measure heavily used by the administration of President Barack Obama in the name of battling terrorism. The Patriot Act passed after the devastating September 11 attacks gave the Federal Bureau of Investigation strong authority to order that people’s telecom records be handed over, without such requests having to be disclosed.