This original paper, based on data from the Erasmus+Blurred Lives Project, presents a new multi-dimensional categorisation model to describe negative online experiences, including forms of cyberbullying, based on a study of internet usage among over N = 2,500 adolescents with lower socio-economic status (SES) backgrounds across five European countries. The paper first sets out the rationale for the development of a new coding system, before describing the current study and nature of the survey data collected. There follows a description of the development of the new system and the series of reliability checks undertaken by the research team (N= 11, from 5 countries) and of the refinements made to the categories and codes. The resulting coding system is presented with consideration of the strengths and limitations, and description of two early pilot studies which have successfully adopted the new system.