The article analyses the legitimacy of citizens telecommunications data retention usage in the fight against terrorism. Data retention, that is the preventive storage of information on the source, data, hour and duration of a connection, type of the connection, communication tool and location of a recipient, is a powerful source of knowledge about citizens and their use should be soundly justified. However, both the European Union and Polish practices show that behind this interference in privacy there is neither a guarantee that the data stored would be used exclusively to fight terrorism and severe crimes, nor a sufficient access control mechanism. The efficiency of data use in the fight against organized crimes, including terrorism, is also dubious.
In her work the author analyses Polish studies concerning information disclosure issues, Internet publications of the European Union and American reports on retention programmes, as well as Polish and foreign positions of non-governmental organizations engaged in the civil rights protection in this respect.