This is patch level 6, which was released a few days ago, so it it should be fine with regards to security. (let me know if you're aware of otherwise)
The reason for 4.0.4 was that we had purchased it some time ago, and only just got around to installing it.
(Their licensing system only allowed me to grab the latest patched version of 4.0.4, to address any security issues)
If there are any notable bugs or issues, we'll buy another license, and update to their latest version.
John