Heres a little Shell Script I wrote which, if run, will check your entire server for insecure versions of wordpress. If it finds any, it will give you the option to upgrade. If you say yes it will backup the existing sites file and database in /root/wp_upgrade and upgrade it.
Please Note: This has not been tested with any wordpress MU instances, and may break them
This has been tested, and will upgrade to version 2.8.4 . If any future upgrade versions come out after this then just change the variable at the top.
It will determine if its a WordPress or WordPress Multi User and apply the correct fix.
If you have any bugs or problems with it, please let me know or contact support
Note: Patched for better portability by valthonis