32 CENTRUM FÖR RÄTTVISA v. SWEDEN JUDGMENT clear, detailed rules on interception of telephone communications, especially as the technology available for use is continually becoming more sophisticated. The domestic law must be sufficiently clear to give citizens an adequate indication as to the circumstances and conditions which give public authorities the power to resort to such measures (Roman Zakharov, § 229). 102. Moreover, since the implementation in practice of measures of secret surveillance of communications is not open to scrutiny by the individuals concerned or the public at large, it would be contrary to the rule of law for the discretion granted to the executive or to a judge to be expressed in terms of an unfettered power. Consequently, the law must indicate the scope of any such discretion conferred on the competent authorities and the manner of its exercise with sufficient clarity to give the individual adequate protection against arbitrary interference (Roman Zakharov, § 230). 103. In its case-law on secret measures of surveillance in criminal investigations, the Court has developed the following minimum safeguards that should be set out in law in order to avoid abuses of power: a description of the nature of offences which may give rise to an interception order; a definition of the categories of people liable to have their communications intercepted; a limit on the duration of the measures; the procedure to be followed for examining, using and storing the data obtained; the precautions to be taken when communicating the data to other parties; and the circumstances in which recordings may or must be erased or destroyed (Roman Zakharov, § 231). 104. As to the question whether an interference has been “necessary in a democratic society” in pursuit of a legitimate aim, the Court has acknowledged that, when balancing the interest of the respondent State in protecting its national security through secret surveillance measures against the seriousness of the interference with an applicant’s rights under Article 8, the national authorities enjoy a certain margin of appreciation in choosing the means for achieving the legitimate aim of protecting national security. However, this margin is subject to European supervision embracing both legislation and decisions applying it. In view of the risk that a system of secret surveillance set up to protect national security may undermine or even destroy democracy under the cloak of defending it, the Court must be satisfied that there are adequate and effective guarantees against abuse. The assessment depends on all the circumstances of the case, such as the nature, scope and duration of the possible measures, the grounds required for ordering them, the authorities competent to authorise, carry out and supervise them, and the kind of remedy provided by the national law. It has to be determined whether the procedures for supervising the ordering and implementation of the restrictive measures are such as to keep the