The hack that spawned this thread was only against VB5. VB3 and VB4 were not vulnerable.
That said it is always important to stay up date on the latest patch/version for whatever branch you are using (3.x branch, 4.x branch. or 5.x branch.)
Emails occasionally don't get delivered so it's also a good idea to check the Announcements forum on vBulletin.com
or the portal here to keep up with major announcements.