A security device placed at a wellhead over a blowout preventer valve, which can be activated to catch a cable and/or a string of pipes upon a cut event or accident, preventing the fall of the same into the well, which includes: an upper horizontal plate and lower horizontal plate, vertically aligned, each having a circular central orifice for the passing of a string of pipes and/or a cable, and a cutout on the front part thereof, located between its front edge and the circular orifice; lateral support device, located between the upper and lower plates, that connect the plates together, delimiting an aperture at the front part of the device that together with the cutouts on the upper and lower plates form a front passage toward the inside of the device; at least two clamps driven by corresponding hydraulic cylinders, which are arranged at an acute angle with the vertical axis of the device; and a movable vertical plate arranged on the front part of the device between the lateral support means, pivotally connected by one of its sides to the upper and lower plates. The movable vertical plate, in a first position, allows for the horizontal passing of a string of pipes and/or cables through the front passage to a location at the center of the device, and in a second position, the movable vertical plate blocks the front passage. In a first position the clamps allow for vertical movement of the string of pipes and or cables and in a second position the clamps block the movement of the same.