From the Ubuntu Forum:

ATTENTION ALL USERS: Malicious Commands

I’d like to take a moment of your time to discuss a recent disturbing trend the staff has been noticing on the forums, and also take this as an opportunity to raise awareness of this situation through education.

We’ve recently had an increase in the number of dangerous commands being posted on the forums. Don’t pretend you don’t know what I mean — commands that cause massive damage or disruption to the user’s computer.

Though I have a bit more than ten years of experience with Linux, I’ve only been using Ubuntu for less than a week, so I was a bit surprised when I was contacted today by Matthew East of the Ubuntu Documentation Project. He had this to say:

Hi,

I’m writing on behalf of the Ubuntu documentation team. I’ve just seen
your guides at http://ubuntology.com/category/howto/. You clearly
share with us an enthusiasm about Ubuntu and a wish to help others get
up and running with the best possible experience.

Found this on the Ubuntu Forum and thought it was worthy of sharing. The person who created it (MenZa on Ubuntu Forum) released it under GPL, so feel free to copy, edit or distribute it. Vector art available here: http://menza.org/upload/ubuntucert.svg