ZBrushCentral

A little problem with "Move" Brush

Hi there! That’s my first day on working ZBrush and i have one question about it. I’l make a face sculp with a tutorial, but there is a problem, when i trying to use a “Move” brush and want to move a little bit a face chapter of shoulders, my back side of arms is change too, how to fix it?

pics or it didn’t happen.

http://docs.pixologic.com/user-guide/3d-modeling/modeling-basics/masking/