Reverser

a polarity reverser

The down grade would give her a start, and then, if Mitchell got his reverser over smartly, he might catch her on the right angle, and she would come back. Mitchell reversed, and moved forward, but to the horror of the fireman, he didn't stop!

Antidebugger techniques are particularly effective when combined with code encryption because encrypting the program forces reversers to run it inside a debugger in order to allow the program to decrypt itself.