Legacy Debian versions and Bash Shellshock

We are running Debian Etch, Lenny and Squeeze because upgrades have never been done in this shop; we have over 150 systems running various Debian versions. In light of the "shell shock" of this week, I assume I need to upgrade bash. I do not know Debian so I am concerned. Can I merely execute apt-get install bash on all of my Debian systems and get the correct Bash package while my repository is pointed at a Squeeze entry. If not, what other course of action do I have?