EN
The terrorist attacks carried out on 11 September 2001 on the World Trade Center and the Pentagon led to the reevaluationof priorities in US security policy. The boundary between freedom and security became more malleable. US intelligenceservices, responsible for security, were set to a state of high alert. To help them in counter-terrorism missions, numerous changesin legislation have been introduced to equip government agencies with additional tools and simplified procedures. The aimof this article is to present the roots, the scope of activities and the scale of exploitation of orders for disclosure of information(the national security letters — NSL) by the Federal Bureau of Investigation (FBI). These orders have caused great controversyon account of the possibility to obtain access to the private data of citizens, while maintaining total secrecy. The radical increasein the number of NSLs issued after 2001 gave rise to many questions, such as: Have national security letters been used for theirintended purpose? Should a total secrecy clause be applied to all NSLs? Have orders of disclosure of information been issuedon the basis of concrete evidence? Has the FBI abused the power given to them? Are NSLs an effective tool in the fight againstterrorism? Why, despite allegations of the violation of human rights and civil liberties, are NSLs still considered a legitimate toolfor the surveillance of society?