Sudo command no longer functions properly When I use the sudo command I get an error message.

sudo: /etc/sudoers is world writable
sudo: no valid sudoers sources found, quitting
sudo: unable to initialize policy plugin


If I try to use chmod on sudoers I get the message "Operation not permitted". Can someone help me fix things so sudo works again?
You should be able to get round this by rebooting into single user mode...


Reboot the computer holding CommandS
The command line should come up showing something about how to mount the drive in write mode mount -uw /, follow these steps.
Now you should be a root user able to edit the /etc/sudoers file.
Issue reboot now to exit and reboot into normal mode.


I don't have a second Mac to test these instructions are step-by-step complete and obviously can't write on the machine while it's rebooting, so please let me know if you get stuck on any steps.