6.0(4)a will give you signature release S317.
Every os update and service pack will give you signatures current as of the date of their release. The software and service pack releases occur every few months. If you need more frequent signature updates, you can purchase a license for your sensors and get the more frequent signature updates. These are release every 10 days on the average.
The most current signature update is S331 released 5/6/08.
