Negative energy in string theory and cosmic censorship violation

We find asymptotically anti--de Sitter solutions in N=8 supergravity which have a negative total energy. This is possible since the boundary conditions required for the positive energy theorem are stronger than those required for a finite mass (and allowed by string theory). But the stability of the anti--de Sitter vacuum is still ensured by the positivity of a modified energy, which includes an extra surface term. Some of the negative energy solutions describe the classical evolution of nonsingular initial data to naked singularities. Since there is an open set of such solutions, cosmic censorship is violated generically in supergravity. Using the dual field theory description, we argue that these naked singularities will be resolved in the full string theory.