Sourcefire - the makers of the open source Snort intrusion detection system - only release intrusion detection rules through subscriptions. However, a number of older intrusion detection rules are available under GPL.
search?q=clearos%2C%20clearos%20content%2C%20dev%2C%20maintainer_dloper%2C%20maintainerreview_x%2C%20keywordfix&btnI=lucky