An improved tamper resistant combination lock with large planar easy to shift blocking slides with spring fingers that fool the lock picker into believing all three positions of the slides are blocking positions, rather than passing positions. The slides block or pass spaced spheroidal obstructions on a plunger. A small bifurcated clip prevents the complete removal of the plunger when all blocking slides are in the pass position. In one embodiment the lock is a padlock-type with a "U" shaped shackle that lies in a common plane with the slides to reduce lock size.