security holes

[Nerius Landys]

I'm running 7.0-RELEASE and I want to defer upgrading to the current
update (currently p9) and/or upgrading to 7.1 for as long as possible.
 I occasionally csup /usr/src and have a gander at /usr/src/UPDATING,
but I don't understand to the fullest extent what security holes may
affect my system.

What do you suggest that I do so that I am informed immediately when I
need to upgrade from 7.0-RELEASE to something else because of a
security hole that affects my system?  How will I know?