An anti-burglary mechanism (6, 6.1) for blocking roller shutters of windows, doors and insect screens in order to prevent unwanted entry of persons into living spaces while the position of the slats of the roller shutter is closed or partially open, comprising a guiding element adapted to be fixed to a side guide (5a, 5b) of the roller shutter and a mouthpiece with an open elongated cut-out, adapted to be inserted into an end of an hollow end slat (2.1) of the roller shutter, wherein the mouthpiece is a flat housing into which a spring with a slider on one side and a guide pin on the other side of it are integrated, whereby the latter can move linearly within the open elongated cut-out, wherein the guiding element is formed by a guide plate and a supporting plate that is perpendicular to the guide plate and that has a mounting hole to be mounted on the wall of a guide channel of the roller shutter side guide (5a, 5b), characterized in that - on the front surface of the guide plate of the guiding element facing the guide channel of the roller shutter side guide (5a, 5b), at least one elongated protrusion is formed, with a conical outgrowth at one end and a slender extension at the opposite end and with at least one depression between them, and that slightly below the elongated protrusion, at least one further protrusion is formed, - at the inner longitudinal edge of the elongated protrusion facing the supporting plate, at least one closed guide channel is formed, which is adjacent to the supporting plate and the further protrusion, while at the outer edge of the elongated protrusion facing a longitudinal cut-out of the guide channel of the roller shutter side guide (5a, 5b) at least one open guide channel is formed, which is adjacent to the longer outer edge of the guide plate, wherein the closed guide channel and the open guide channel are interconnected, - the closed guide channel is funnel-shaped and further passes into a winding section with at least three curves, the further protrusion together with the elongated protrusion forms the middle winding section of the closed guide channel, the last curve of the winding section at the further protrusion turns round the slender extension and goes further into the open guide channel, - the edges of the elongated protrusion represent five rigid sliding surfaces (15a, 15b, 15c, 15d, 15e), whereby the first and second sliding surfaces (15a, 15b) lie at the closed guide channel, whereas the third, fourth and fifth sliding surfaces (15c, 15d, 15e) lie at the open guide channel, - along the winding section with at least three curves within the closed guide channel at least three blocking spots (14a, 14b, 14c) are formed, whereby the first blocking spot is located within the first curve, the second blocking spot within the second curve and the third blocking spot within the third curve of the closed guide channel, - the mouthpiece has on the front surface of its head facing the wall of the guide channel of the roller shutter side guide (5a, 5b) on which the supporting plate is to be mounted and at the elongated cut-out at least one sliding ridge. - on the front surface of the guide plate of the guiding element facing the guide channel of the roller shutter side guide (5a, 5b), at least one elongated protrusion is formed, with a conical outgrowth at one end and a slender extension at the opposite end and with at least one depression between them, and that slightly below the elongated protrusion, at least one further protrusion is formed, - at the inner longitudinal edge of the elongated protrusion facing the supporting plate, at least one closed guide channel is formed, which is adjacent to the supporting plate and the further protrusion, while at the outer edge of the elongated protrusion facing a longitudinal cut-out of the guide channel of the roller shutter side guide (5a, 5b) at least one open guide channel is formed, which is adjacent to the longer outer edge of the guide plate, wherein the closed guide channel and the open guide channel are interconnected, - the closed guide channel is funnel-shaped and further passes into a winding section with at least three curves, the further protrusion together with the elongated protrusion forms the middle winding section of the closed guide channel, the last curve of the winding section at the further protrusion turns round the slender extension and goes further into the open guide channel, - the edges of the elongated protrusion represent five rigid sliding surfaces (15a, 15b, 15c, 15d, 15e), whereby the first and second sliding surfaces (15a, 15b) lie at the closed guide channel, whereas the third, fourth and fifth sliding surfaces (15c, 15d, 15e) lie at the open guide channel, - along the winding section with at least three curves within the closed guide channel at least three blocking spots (14a, 14b, 14c) are formed, whereby the first blocking spot is located within the first curve, the second blocking spot within the second curve and the third blocking spot within the third curve of the closed guide channel, - the mouthpiece has on the front surface of its head facing the wall of the guide channel of the roller shutter side guide (5a, 5b) on which the supporting plate is to be mounted and at the elongated cut-out at least one sliding ridge.