A portable electronic device requiring securing against theft, includes a cavity with an opening thereinto. The opening is accessible at an exterior of the device, and defined by an upper edge, a juxtaposed lower edge, and a pair of juxtaposed side edges. The cavity is defined by an upper wall, a juxtaposed lower wall, and juxtaposed side walls, the side walls being angled relative to each other with a separation distance between them gradually increasing in a direction into said cavity, away from said opening into said cavity, whereby a planar cross section through the cavity that bisects both side walls has a trapezoidal shape. The lock opening has a size and shape slightly larger than the cross-sectional size of the forward section of a locking element and an interior larger in cross-sectional size than at the opening of the cavity.