Imposing order on program statements to assist anti-virus scanners

A metamorphic virus applies semantics preserving transformations on itself to create a different variant before propagation. Metamorphic computer viruses thwart current anti-virus technologies that use signatures - a fixed sequence of bytes from a sample of a virus - since two variants of a metamorphic virus may not share the same signature. A method to impose an order on the statements and components of expressions of a program is presented. The method, called a "zeroing transformation," reduces the number of possible variants of a program created by reordering statement, reshaping expression, and renaming variable. On a collection of C program used for evaluation, the zeroing transformation reduced the space of program variants due to statement reordering from 10/sup 183/ to 10/sup 20/. Further reduction can be expected by undoing other transformations. Anti-virus technologies may be improved by extracting signatures from zero form of a virus, and not the original version.