Data retention, a balance between judicial requirements and the risk of illegality

Whenever a telephone or a computer device connected to the network is used, the telecommunication service providers keep some data, e.g. the origin of the communication, its destination and its size. The prior storage activity of telephone traffic data and electronic communications traffic data is defined as "data retention" and can play a fundamental role for investigative purposes. This article aims at recognizing the benchmarks for regulation of data retention that respects the proportionality principle. As part of this analysis, an approach that also takes into account the right to the defense of the accused is proposed. Furthermore, the article disputes the possibility of ab origine define the data retention period on the basis of the type of crime. This is because the internet service provider cannot know a priori what kind of crime will be combined with any given data, until access to that data is requested by the competent national authorities.