The odd part is you're acting like linux isn't inherently secure. While I will grant you, it isn't perfect out of the box, a small amount of configuration can make it very secure for your needs.
You're not dealing with Windows here, where it constantly needs to check in, in order to know what the hell is going on. I would recommend a secure setup of LDAP for account information (pick your openldap flavor, Fedora Directory Server works great here), and a kerberos server for passwords.
I would also like to point out the "commercial" Red Hat Satellite server, or the open/free Spacewalk server to manage all servers at once, like you can do with AD.
A refreshing bipartisan effort to return Fair Use to it's rightful place as the law of the land. (for media content, anyway)"Today, Reps. Rich Boucher (D-Va.) and John Dolittle (R-Calif.) introduced what they call the "Freedom and Innovation Revitalizing U.S. Entrepreneurship" (or FAIR USE) Act they say will make it easier for digital media consumers to use the content they buy.
Machines have less problems. I'd like to be a machine. -- Andy Warhol