Lithuania recently has made public the KGB archives as related to Lithuania. This includes the structure of the organization and the people who worked there. The names of those who have not stepped forward and declared what they did are made public. For example, one of the departments has this lengthy list. It is said that some of the archives were destroyed or moved to Moscow during the last days of the Soviet power in Lithuania.
The KGB was the organization that everyone feared. They could decide that one is not loyal to the state and put that person to prison for some reason - for example "treason". A milder case would be that they would deem a person untrustworthy and basically ruin any career or professional possibility for him/her and their family - as everything was state owned - and one could not hire a person without KGB approval.
As a note aside - it is interesting to note that the predecessor of this organization was Cheka - which in turn was established and run by no other than Felix Dzerzhinsky - a person who spent his youth in Vilnius and Kaunas (Wikipedia uses Russian version - Kovno).