However, it is the classified (secret) activities for which it was really feared. This was the work of the Main Directorate for State Security, known as the GUGB. The NKVD also included the Soviet secret police. The GUGB protected the state security of the Soviet Union. This was done by massive political repression, including the use of sanctioned political murders and assassinations, especially in the era of Joseph Stalin, during the Great Purge. 