The first time I decided to hack around a bit:D

One of my teachers made a quiz software, which is only used by him(his lectures are about databases), and it is highly unsecure. When I heard that it is written in C# I decided to look in it's source code. The biggest problem I ran into: this program is only available on the computers in his classroom, and he monitors the computers display. However, I successfully put it into my pendrive without getting caught.

So when I got home, I just had to use a .NET decompiler(in this case: dotPeek) to get the fully functional source code. The basic function of the program was to download a quiz from his database server, and when it was finished, grade it client-side. Than, I realized how bad it was: It contains the number of questions, the number of correct and incorrect answers.
I've just made a modified .exe, which contained really little modification(like correctAnswers=maxQuestions, incorrectAnswers=0). Everything looks the same, you just have to click over it, and everytime it will return with 100%.

And the bonus: The program connects to the database as a user with root access, and without password. I was able to log in, download(dropping was available too, but didn't try) databases(with all the answers) and so on.

Never had to use it though, it was just a sort-of experience gaining.:)