Protective device for covering window openings on a temporary basis, comprising at least one telescopic rod to which four adjustable plates consisting of two upper plates each comprising an upper horizontal groove and two lower plates each comprising a lower horizontal groove, are attached using fastening points on the rod, which are inserted in said horizontal grooves of the upper and lower plates, allowing for the adjustment of the height of the four plates by extending or retracting the rod, and adjusting the width of the four plates by moving the plates to one side or the other, sliding them with the fastening points in the horizontal grooves; and wherein the rod comprises two sections (21,22) of tubing, an upper tubing section and a lower tubing section; and wherein the two upper plates are arranged to be raised or lowered to adjust the height to the size of the opening to be covered, extending or retracting the upper tubing section of the rod with regard to the lower tubing section, and both the upper plates and lower plates can be separated more or less in order to adjust the width of the opening by sliding them to one side or the other with the three fastening points in the horizontal grooves; and wherein the lower plates are also fitted with vertical grooves, at least on the outer side of each one, which are designed to receive additional fastening points provided at the outer ends of the two upper plates whereby the upper and lower plates are joined together by their respective outer ends, the device being characterised in that each lower plate also comprises an upper horizontal groove; and in that the fastening points of the device comprise three fastening points, one upper fastening point at the end of the upper tubing section, one central fastening point and one lower fastening point at the lower tubing section; and in that the upper fastening point is inserted in the upper horizontal grooves of the two upper plates, whereas the central fastening point and the lower fastening point are inserted in the upper and lower horizontal grooves of the two lower plates respectively. wherein the rod comprises two sections (21,22) of tubing, an upper tubing section and a lower tubing section; and wherein the two upper plates are arranged to be raised or lowered to adjust the height to the size of the opening to be covered, extending or retracting the upper tubing section of the rod with regard to the lower tubing section, and both the upper plates and lower plates can be separated more or less in order to adjust the width of the opening by sliding them to one side or the other with the three fastening points in the horizontal grooves; and wherein the lower plates are also fitted with vertical grooves, at least on the outer side of each one, which are designed to receive additional fastening points provided at the outer ends of the two upper plates whereby the upper and lower plates are joined together by their respective outer ends, the device being characterised in that each lower plate also comprises an upper horizontal groove; and in that the fastening points of the device comprise three fastening points, one upper fastening point at the end of the upper tubing section, one central fastening point and one lower fastening point at the lower tubing section; and in that the upper fastening point is inserted in the upper horizontal grooves of the two upper plates, whereas the central fastening point and the lower fastening point are inserted in the upper and lower horizontal grooves of the two lower plates respectively.