User-defined rules refer to rules that an end user writes specifically for their environment. These rules are not contributed back to the open source community. When writing your own rule, a SID higher than 1,000,000 should be assigned. Snort encourages the submission of user-defined rules back to the community for inclusion in the community ruleset. If you wish to contribute, please send your rules along with and packet captures of the data to the Snort-sigs mailing list: Found here.