Embodiments of the invention provide a method and a system of detecting source code in a message being sent over a digital communication network to secure against unauthorized leakage of source code. The message is intercepted on a network device, placed into a memory on the network device, and divided into one or more segments, wherein each segment includes a predetermined number of lines of text from the message. For each segment, one or more syntax rules of a programming language is applied to the segment and a predetermined number of context lines of text before the segment and/or after the segment, to determine which of the syntax rules of the programming language are matched in the segment. A determination of whether the text message includes source code is provided based on the syntax rules that were matched.