A method and system for transmitting a media stream of data from a sending client terminal to a receiving client terminal, the terminals being arranged in a protected computer environment including at least one protective unit in association with a data forwarding element. The protective unit is intended to protect the receiving client terminal from data transmitted from unauthorized sending clients. The method includes: transmitting authorization data from the receiving client terminal to sending client terminal via the protective unit for instructing the unit to allow return of a media stream from the sending client terminal to the receiving client terminal during a predetermined period of time. Moreover, the method includes the step of: the receiving client terminal is adapted to independently transmit authorisation data via the protective unit at shorter intervals than the predetermined period of time for maintaining the allow return mode of the protective unit.