A software birthmark is a unique characteristic of a program that can be used as a software theft detection technique. In this paper we present and empirically evaluate a novel birthmarking technique - Whole Program Path Birthmarking -which uniquely identifies a program based on a complete control flow trace of its execution. To evaluate the strength of the proposed technique we examine two important properties: credibility and tolerance against program transformations such as optimization and obfuscation. Our evaluation demonstrates that, for the detection of theft of an entire program, Whole Program Path birthmarks are more resilient to attack than previously proposed techniques. In addition, we illustrate several instances where a birthmark can be used to identify program theft even when an embedded watermark was destroyed by program transformation. software piracy, copyright protection, software birthmark.