"Sourcefire subscription customers get closed-source
versions of the rules, which they are not allowed to distribute
under any conditions, as soon as they are available. After 30 days,
the Vulnerability Research Team (VRT) rules (verified by
Sourcefire) are released under the GPL to anyone who registers and
downloads them. Other rules, developed by the open source
community, are available as well, under whatever license the
creator has released them."