Error when using sudo

hi
when i use sudo I see this error

root@asecurity:/home/arashsoft# sudo
sudo: error in /etc/sudo.conf, line 0 while loading plugin `sudoers_policy'
sudo: /usr/lib/sudo/sudoers.so must be only be writable by owner
sudo: fatal error, unable to load plugins


why

i found out by myself

step1: remove sudo

apt-get autoremove sudo
apt-get autoclean sudo
apt-get autoclean
reboot

step2: install sudo
apt-get install sudo
apt-get autoclean sudo
apt-get autoclean
reboot


Add your username to the sudo group
- Type in the following command...
adduser yourusernamehere sudo
- then press [enter]

Now add your name to /etc/sudoers file
- Type in the following command...
nano /etc/sudoers
- then press [enter]
- Scroll down and look for the line "%sudo ALL=(ALL:ALL) ALL"
- Below that line type in the following...
yourusernamehere ALL=(ALL:ALL) ALL
- Press "Ctrl+x" then press "y" and then press [enter] to exit and save the file

Now we exit out of the Terminal completely
- Type in the following command...
exit
- then press [enter]
- Type exit again...
exit
- then press [enter]
- That should have closed the Terminal application

Now let's open a new Terminal and test to see if sudo is working for your user name
- Test sudo by typing the following command...
sudo ls
- then press [enter]
- type in your password and press [enter]

- If the output looks like the following...
yourusernamehere is not in the sudoers file. This incident will be reported.
- then you might have to start from the beginning of these instructions and try again.

- If the output looks like this...
Desktop Documents Downloads Music Pictures Public Templates Videos
- Your username now has sudo rights, congratulations!