Wordpress only has one track, which is the only one that gets updates. Once a new major release is available all support for the previous release ends. If you want the most secure version you need to be on the latest (4.2.2).
Um, no? They do security updates for the last couple of versions of Wordpress. They even extend that to the last couple versions of their stock theme when they require an update.
https://codex.wordpress.org/WordPress_Versions