How is the Snort software licensed?

The Snort engine continues to be distributed under the free software/open source GNU General Public License version 2 (commonly known as the “GPL v.2”). With the GPL license, Snort is available free of charge. Users may download the software for free and modify, integrate, and distribute it. However, GPL users must abide by the rules of the GPL, which stipulates that if a Snort-derived application is redistributed, the complete source code for this application must also be open and available for redistribution.