Human Intelligence – HUMINT
Human intelligence is the oldest method of information gathering and it is the queen of intelligence activity. It is based on the concealed use (finding, controlling, tasking) of co-operators of various types, informers and agents (the Czech legal language uses the term "person acting for the benefit of secrete services"). It is the obtaining of information "from and through human sources". It is the only and irreplaceable method which can notice the plans and intentions of monitored persons before they take the first steps leading to its realisation.
The operatives work with the help of service technology - telecommunications tapping (in legal states it is subject to the approval procedure, as it is a very serious interference with rights and freedoms) and physical surveillance.
HUMINT is the most effective method but also the most dangerous one and its results come slowly; it brings advantages and disadvantages of the "human factor".
Source: Petr Zeman - lectures, trainings and public speeches