A mathematical model of the dynamics of changes in the state of security indicators of control and diagnostic data on the technological process is proposed. It is constructed using Markov chains and takes into account the probabilistic-temporal mechanism for changing the state of data protection indicators of this class. Based on this model, a methodological approach has been developed for multi-criteria assessment of the security of control and diagnostic data on the technological process. The approach is based on the analysis of current deviations of the values of data protection indicators from the requirements for them, takes into account and eliminates the uncertainty of the initial diagnostic information. The proposed methodological approach also allows one to take into account transients that affect security when introducing control over the structure, parameters and modes of collection and processing of control and diagnostic data about the technological process in various conditions.