Current malware detection and classification tools fail to adequately address variants that are generated automatically using new polymorphic and metamorphic transformation engines that can produce variants that bear no resemblance to one another. Current approaches address this problem by employing syntactic signatures that mimic the underlying control structures such as call- and flow-graphs. These techniques, however, are easily defeated using new program diversification techniques. This hampers our ability to defend against zero day attacks perpetrated by such auto “replicating”, rapidly spreading malware variants. In this paper, we present a new form of abstract malware signature generation that is based on extracting semantic summaries of malware code that is immune to most polymorphic and metamorphic transformations. We also present results of our initial, experimental evaluation of the proposed approach.