2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/163413A riemannian manifold is secure if the geodesics between any pair of points in the manifold can be blocked by a finite number of point obstacles. Compact, flat manifolds are secure. A standing conjecture says that these are the only secure, compact riemannian manifolds. The conjecture claims, in particular, that a riemannian torus of any dimension is secure if and only if it is flat. We prove this for two-dimensional tori.15 pages, 4 figuresDynamical SystemsDifferential Geometry37D40, 37E99, 53C22text