A tamper evident bolt security seal comprising: a bolt comprising a shank having opposing ends, a head at one shank end and a locking groove in the shank surface at the other shank end forming a shank locking portion; and a locking unit to which the shank locking portion is secured; the locking unit comprising: first and second mating housing portions (14, 12) forming a housing defining an inner chamber; the first housing portion including a first peripheral side wall; the second housing portion including a second peripheral side wall having top and bottom regions, the second housing portion including a top wall and a bottom wall attached to the side wall respective top and bottom regions, characterized by: the top wall having an aperture for receiving the shank therethrough; the first peripheral side wall being captured between the top and bottom walls (18, 16) and cooperating with the mating second housing portion for forming the inner chamber; a lock body secured to the first housing portion in the inner chamber and arranged for receiving the shank locking portion, the lock body having a locking channel adjacent to the received shank locking portion; a resilient element in the locking channel cooperating with the shank locking groove for locking the received shank to the lock body; and a cover arranged for the shank locking portion to pass therethrough for said locking and secured to the bottom wall, the cover and bottom wall for enclosing the first housing portion and the top and side wall of the second housing portion whereby the locked shank and lock body interlock the first and second housing portions (14, 12) thereto. a bolt comprising a shank having opposing ends, a head at one shank end and a locking groove in the shank surface at the other shank end forming a shank locking portion; and a locking unit to which the shank locking portion is secured; the locking unit comprising: first and second mating housing portions (14, 12) forming a housing defining an inner chamber; the first housing portion including a first peripheral side wall; the second housing portion including a second peripheral side wall having top and bottom regions, the second housing portion including a top wall and a bottom wall attached to the side wall respective top and bottom regions, first and second mating housing portions (14, 12) forming a housing defining an inner chamber; the first housing portion including a first peripheral side wall; the second housing portion including a second peripheral side wall having top and bottom regions, the second housing portion including a top wall and a bottom wall attached to the side wall respective top and bottom regions, the top wall having an aperture for receiving the shank therethrough; the first peripheral side wall being captured between the top and bottom walls (18, 16) and cooperating with the mating second housing portion for forming the inner chamber; a lock body secured to the first housing portion in the inner chamber and arranged for receiving the shank locking portion, the lock body having a locking channel adjacent to the received shank locking portion; a resilient element in the locking channel cooperating with the shank locking groove for locking the received shank to the lock body; and a cover arranged for the shank locking portion to pass therethrough for said locking and secured to the bottom wall, the cover and bottom wall for enclosing the first housing portion and the top and side wall of the second housing portion whereby the locked shank and lock body interlock the first and second housing portions (14, 12) thereto.