Comment 10 for bug 244093

I've detected the problems:
1) the checkbox for its status (checked/unchecked) looks for "http://archive.ubuntu.com" instead of "http://security.ubuntu.com"
2) if again you uncheck and check the hardy-security after switching back to "archive.ubuntu.com", it will add the hardy-security with "http://security.ubuntu.com", which will show as non-canonical third-party software repository

Execute in terminal: gksu /etc/apt/sources.list

Change any occurence security.ubuntu.com to archive.ubuntu.com

For example, I changed:
deb http://security.ubuntu.com/ubuntu/ hardy-security universe main multiverse restricted
deb-src http://security.ubuntu.com/ubuntu/ hardy-security universe main multiverse restricted

..to:
deb http://archive.ubuntu.com/ubuntu/ hardy-security universe main multiverse restricted
deb-src http://archive.ubuntu.com/ubuntu/ hardy-security universe main multiverse restricted

..things will be back to normal:

Don't uncheck and check the checkbox in Software Sources > Updates again, it will cause the same problem