Take a look at the top-voted answers to "How to explain Heartbleed without technical terms?" on security.SE and repeat that:
http://security.stackexchange.com/questions/55343/how-to-exp...
http://security.stackexchange.com/questions/55343/how-to-exp...
It takes a special skill to eliminate all the non-essential information and produce something truly simple to understand, like the comic.
The only reason I ever manage to be short in text form is being able to go back and delete.