A security device for a cargo van comprises a sheet metal grill stamped or laser cut to exhibit a plurality of regularly spaced apertures therethrough and surrounded by a solid border having a plurality of notches formed inward of the border into which are fitted clamp members for securing the grill in place against a window of the cargo van to inhibit break-ins and theft of articles carried by the van. The clamp members include U-shaped sockets adapted to cooperate with the notches formed in the border and base members for secure attachment of the clamp members to a frame of the window using self-tapping screws.