An arrangement comprising a core wall with recesses for a window or a door, a window frame or a door frame fitted into the recesses for a window or a door and a mounting system for a movable installation in front of the window or the door such as roller shutters, external venetian blinds etc., including a support device fitted into the core wall on the inside, attached to the core wall and to the window frame or door frame and adapted to hold the installation in front of the window or the door, an outer cover connected to the outside of the core wall and comprising at least one reinforcing layer made of a high-strength, tough material and fastening members by means of which at least the reinforcing layer is attached to the core wall, the reinforcing layer being connected to the core wall by means of the fastening members along its upper edge and the two side edges (24, 25), characterized in that a burglar-inhibiting outer cover is provided which satisfies at least the following conditions: A) the reinforcing layer has a strength which, for a width of the window frame or door frame of up to 1.50 m, corresponds to at least 90% of the strength of a 0.88 mm thick steel sheet with an identical contour of the reinforcing layer and, for a width of the window frame or door frame of more than 1.50 m, corresponds to at least 80% of the strength of a 1.5 mm thick steel sheet with identical contour of the reinforcing layer, and B) the fastening members by means of which the reinforcing layer is fastened to the core wall are present in at least a number Y, wherein Y is defined by the following formula: Y = L 0 ⋅ mm 6 ⋅ Z P 2 + L S 1 + L S 2 ⋅ mm 2 ⋅ Z P 2 − 4 and the distance of the fastening members at the upper edge of the reinforcing layer is at most 400 mm, and L O is the length in mm of the upper edge of the reinforcing layer, L S1 is the length in mm of the first side edge of the reinforcement layer, L S2 is the length in mm of the second side edge of the reinforcing layer, and Z P is the geometrical parameter in mm relevant for the tensile strength, such as nominal diameter, etc., of the fastening members by means of which the reinforcing layer is fastened to the core wall, and at least one of the following conditions can be satisfied: C) at least some of the fastening members by means of which the reinforcing layer is fastened to the core wall are anchored to the core wall in a depth of at least (3-a) times the geometric parameter relevant for the tensile strength, such as nominal diameter (Z P) etc., of the fastening member wherein a is 1.0 when the core wall is for instance made of concrete, 2.0 when the core wall is for instance made of sand-lime brick or solid brick and 2.4 when the core wall is for instance made of pumice, lightweight concrete or softwood, and D) the reinforcing layer is fastened by the fastening members in a floating manner to compensate for thermal expansion. A) the reinforcing layer has a strength which, for a width of the window frame or door frame of up to 1.50 m, corresponds to at least 90% of the strength of a 0.88 mm thick steel sheet with an identical contour of the reinforcing layer and, for a width of the window frame or door frame of more than 1.50 m, corresponds to at least 80% of the strength of a 1.5 mm thick steel sheet with identical contour of the reinforcing layer, and B) the fastening members by means of which the reinforcing layer is fastened to the core wall are present in at least a number Y, wherein Y is defined by the following formula: Y = L 0 ⋅ mm 6 ⋅ Z P 2 + L S 1 + L S 2 ⋅ mm 2 ⋅ Z P 2 − 4 and the distance of the fastening members at the upper edge of the reinforcing layer is at most 400 mm, and L O is the length in mm of the upper edge of the reinforcing layer, L S1 is the length in mm of the first side edge of the reinforcement layer, L S2 is the length in mm of the second side edge of the reinforcing layer, and Z P is the geometrical parameter in mm relevant for the tensile strength, such as nominal diameter, etc., of the fastening members by means of which the reinforcing layer is fastened to the core wall, and and the distance of the fastening members at the upper edge of the reinforcing layer is at most 400 mm, and L O is the length in mm of the upper edge of the reinforcing layer, L S1 is the length in mm of the first side edge of the reinforcement layer, L S2 is the length in mm of the second side edge of the reinforcing layer, and Z P is the geometrical parameter in mm relevant for the tensile strength, such as nominal diameter, etc., of the fastening members by means of which the reinforcing layer is fastened to the core wall, and C) at least some of the fastening members by means of which the reinforcing layer is fastened to the core wall are anchored to the core wall in a depth of at least (3-a) times the geometric parameter relevant for the tensile strength, such as nominal diameter (Z P) etc., of the fastening member wherein a is 1.0 when the core wall is for instance made of concrete, 2.0 when the core wall is for instance made of sand-lime brick or solid brick and 2.4 when the core wall is for instance made of pumice, lightweight concrete or softwood, and D) the reinforcing layer is fastened by the fastening members in a floating manner to compensate for thermal expansion.