Tamper-resistant lock

The invention provides a lock having a thick U-shaped shackle, a transverse housing for receivably locking extending ends of the shackle, a pair of longitudinal members which lockably intersect the shackle ends and which are actuated by a lock protected within the intermediate portion of the housing. In an exemplary embodiment of the invention, the shackle and housing are constructed of substantially thick tubular metal, and the shackle ends may be conformed to openings in the housing. The longitudinal members may be extended post members which intersect inserted shackle ends or may be forked members which slidably engage flat portions on inserted shackle ends. The locking mechanism may be activated through a rack-and-pinion, cam-and-pin, or similar assembly, and may further comprise shackle ends having flat sections conformed to the housing openings to prevent rotation. The compact and integral design affords improved resistance to tampering such as by shattering or cutting/twisting methods.