I am guessing you are using an .htaccess or iptables for the ip ban? That has nothing to do with the software and you should be fine.
Any version under the current version could be a risk. Just like your computer, web server software it is strongly recommended and advised to stay up to date with current versions.
If looked at the old change logs, you will see many bugfixes. Those could also have some security security fixes as well. There was a lot changed from v7.01 to v7.3 and probably would have been a lot to find and patch.
I think there should be a time that version numbers reach and EOL for support such as patches and stuff as its harder on the developers to keep so many versions up to date.
