Without action on your part, legacy TurnKey 12 / Debian 6.0 (AKA Squeeze) based systems will no longer receive automatic security updates. Next time there is a remotely exploitable security vulnerability your system could get compromised.

If you're not ready to upgrade to Debian 7.0 you may want to consider manually enabling the new (experimental) LTS security updates.

Read more:

http://www.turnkeylinux.org/blog/extending-squeeze-security-support