sudo tidak meminta password?

Periksa file /etc/group dan periksa apakah user tersebut adalah group dari sudo. Hapus nama user dari group sudo dan selanjutnya, bila user menggunakan sudo, akan meminta password dan setelah berhasil memasukkan password, muncul pesan:

We trust you have received the usual lecture from the local System
Administrator. It usually boils down to these three things:

#1) Respect the privacy of others.
#2) Think before you type.
#3) With great power comes great responsibility.

Selamat ber-paranoid ria!

PS:
Thx for bertilow in ubuntu forum
http://ubuntuforums.org/showthread.php?t=100274