Quote:
I examine my hard disk drive with a hex editor
What exactly did you type?
Does your system still work?
Let's hope that this is a personal system and that any accidental damage will only affect yourself.
One of the first rules of typing commands is: "If you don't know what is going to happen, do not type the command".
Explanation of what happened. The random binary code which you were looking at coincidentally contained screen control codes. These messed up your display.
It's not a virus.
Hint: While you are learning, don't use the root account.