An anti-piracy device for ships comprises a blocking device, such as a metal plate, to block an opening from the exterior to the interior of a ship, such as a window or porthole. The anti-piracy device also includes mounts, which are mounted permanently to the interior wall of the ship, to which the blocking device can be removably fastened, by nuts or the like. This allows the device to be installed when entering dangerous waters, but removed and stored when traversing safe waters.