What does C or not C have to do with an external drive? Absolutely nothing. A secondary partition whether on the
same drive or not would have exactly the same effect.

You don't even grasp what "secure" means. The vulnerabilities
in question where effective for about a year - with seemingly
nobody knowning them. All this time your "security measures"
only worked by chance and pure luck. If you had shared anything on C or installed LimeWire on the same drive as
your shared files you would have been ****ed like everyone
else. Security must be based on a concept not on a stupid
hack or workaround. Use the core functionality of your operating system. Account management and file permissions are
well-known and understood security devices since the 70s.
You don't have a ****ing clue whether LimeWire has a bug
that allows execution of random data or access to any file
on your system. Your external hdd will in no way protect you
against such bugs. Using a dedicated user account and appropriate file permissions would make you immune against
such bugs i.e., they couldn't cause you any serious trouble.

If you think such precautions are overkill or too much trouble, well nobody forces you to use them. However, don't
make false claims about security then, you are NOT secured.

And your stupid useless virus scanner and personal firewall
are nothing but snake oil devices to provide little more
than pseudo-security whilst providing additional attack paths.

So stop spreading false information.