An apparatus (fig. 11) for preventing theft of portable equipment like computers is disclosed. The equipment must be provided with a special rectangular slot (fig. 5). An attachment mechanism includes a housing (36) for a spindle (46) having a first portion rotatable within the housing, a shaft (52) extending outwardly from the housing, and a crossmember (54) at the end of the shaft (52) having dimensions conforming to those of the slot. An abutment mechanism (60) also emanates from the housing (36). The combined dimensions of the abutment mechanism (60) and the shaft (52) closely conform to the dimensions of the slot. The crossmember (54) is aligned with the abutment mechanism (60) so that the crossmember (54) can be inserted through the slot with the shaft (52) and the abutment mechanism occupying the slot. The spindle (46) is then rotated 90 degrees to misalign the crossmember (54) with the slot to attach the mechanism. A cable (18) is secured to the housing and to an immovable object.