The cosmic censorship conjecture roughly states that singularities in the evolution of spacetime are always hidden from the outside world by event horizons. As a test for this conjecture Penrose proposed the inequality $M\geq\sqrt{A/16\pi}$, relating the total ADM mass M of a spacetime to the area A of an event horizon. For time symmetric initial data sets of Einstein's equations this inequality has been confirmed, independently by Huisken and Ilmanen (for one black hole) and by Bray (for multiple black holes). In this talk we will show how the time symmetric proofs can be generalized to apply to general initial data, assuming existence for a canonical system of partial differential equations. This will entail the introduction of a new method for deforming initial data sets, which in its most general form should have several other applications; these include the existence problem for black holes and quasi-local mass. This is joint work with Hubert Bray.