I used to teach C and C++ programming at University of Colorado, Denver.
Seems like I fail a student a semester for copying source code from a book or somewhere. Source is kind of an individual thing ya know. Typically, I spot it when I get deja vu grading a paper - then go back to find the other one that reminded me of it.
In all cases but one, I've had full backing of the department head. In only one case did the student's advocate give me a hard time (and he is a jerk and my department head still backed me).
My policy is that its not possible to pass the class with uncompleted assigments and you get a zero on any assignment that I can prove is not your own work.
We've gone soft on this.
In my parents' day, plagarism could get you expelled from the college permanently. It should still do that.