In this talk we will discuss the use of Steganography (hiding the fact that two parties are communicating, or hiding a secret message within an innocuous one) for tracing software pirates. Watermarking represents a particular use of steganography where the hidden message is a copyright notice or a customer identification number, and the innocuous (cover) message is a digital image, an audio file, or a video clip. For example, inside a song file downloaded from iTunes may be hidden the credit card number of the customer, allowing the copyright owner to trace a pirated copy of a song back to the person who originally purchased it. Watermarking doesn't prevent illegal copying of media, but rather allows the tracing of pirates after the fact. In this talk we will discuss the watermarking of software. That is, we are interested in embedding a secret mark inside a computer program to allow us to trace software pirates. We will see how several watermark embedding algorithms have been designed based on graph problems such as graph coloring and graph enumerations.