The talk presents an ongoing project about the historical developments of tracking on the Danish web. Tracking of web users and their behaviour online is carried out using a multitude of different technologies and for a lot of different purposes from authorisation and personalisation over web analytics and optimisation to targeted advertising and social profiling. The extent of tracking and data collection, especially by powerful companies like Facebook and Google, have caused concerns about privacy and consent. The project attempts to map the use of different tracking technologies and companies involved in tracking on the Danish web from 2006 to 2015. The materials used are from the Danish national web archive Netarkivet, and the large-scale analyses are performed using the supercomputer DeiC National Cultural Heritage Cluster (both are located at the Royal Danish Library). The general idea of the project is to use the archived source code of websites to find traces of tracking. The presentation will show different ways of exploring the source code and experimenting with computational methods to find these traces and discuss the main methodological challenges involved.