A/HRC/8/13 page 10 absolutely necessary in order to prevent terrorist acts. Intelligence-gathering activities, in particular covert surveillance activities, must be regulated by law, monitored as much as possible by independent agencies, and subject to appropriate judicial review. Under international human rights law, any act which impacts upon a person’s privacy must be lawful; it must be prescribed and regulated by law. This means that any search, surveillance activity, or data collection about a person must be clearly authorized by law. The extent to which this is allowed to occur must not be arbitrary or left to discretionary authority. The law authorizing interference with privacy must specify in detail the precise circumstances in which the interference is to be permitted, and must not be implemented in a discriminatory manner. 25. All measures taken by law enforcement agencies to combat terrorism must be lawful, both under national and international law. Recent counter-terrorist strategies have often included efforts to collect, analyse and use information about large numbers of individuals. In recent years, many States have significantly expanded the surveillance powers and capacity of their law enforcement agencies. These practices all have the potential seriously to limit the privacy of the individuals concerned. Those measures also raise questions about how the data thus collected are to be protected, stored, and, when necessary, shared with other agencies of the same Government or indeed other jurisdictions. When personal information is collected, it must be protected against unlawful or arbitrary access, disclosure, or use. 26. Human rights concerns which may arise during the course of information gathering or evidence sharing include the impact of the sources of intelligence information on its admissibility as evidence; differences in the definition of the elements of terrorist crimes between jurisdictions, as well as “dual criminality” and legality concerns; the procedures for gathering evidence, in particular where interrogation of witnesses or suspects is coercive, involving torture or cruel, inhuman and degrading treatment; the rules relating to the use of confession evidence, particularly where the confession was obtained under duress; appropriate access to classified and secret information by the accused and his or her defence; unlawful interferences with privacy with respect to interception, search and seizure, surveillance; protection of witnesses as sources of such evidence; questions related to the appropriate burdens of proof in legal proceedings; and the overarching right to an effective remedy for violation of human rights in the context of evidence-gathering and information-sharing. 27. I appreciate that techniques such as electronic surveillance, undercover operations and controlled deliveries may be effective in preventing and combating terrorist acts. However, domestic arrangements and legislation relating to these techniques must be reviewed to reflect technological developments, taking full account of any human rights implications and the need to facilitate international cooperation. New technological developments and modern methods of investigation have created new concerns with respect to the legitimacy in human rights terms of certain methods and the protection of the rights of the individuals involved in the course of an investigation conducted further thereto. The police, prosecutors and the courts have a duty to ensure that these methods are used lawfully and in accordance with applicable human rights standards. 28. The sharing of information and intelligence between States has raised concerns for national prosecutors and courts. There are notably questions around the admissibility of evidence collected in other States through methods that would not necessarily be acceptable in their own State, as well as the use of evidence obtained by officials in another State in violation of the law