When I was teaching information security, I literally had more than half of my students turn in heavily plagiarized papers. It was pretty easy to spot suspicious phrases, and Googling would always turn up the sources quickly.
It was actually quite overwhelming figuring out how to deal with it all - the problem was if we gave no marks for that paper, or failed all the students, it would've been pretty disastrous for the university. In the end, we had to punish the most egregious plagiarism with no marks, and give partial marks for the rest, trying to identify and give credit for the original work.
I had not one, but several students come and argue they should get their full marks back, "for fulfilling the requirements of the assignment".