My teacher had tricks to know who copied the assignment

I had so much fun attending classes even though lectures explained by teachers were boring I still manage to have some crispy tipsy enjoyment. Throwing things to each other, leaving the classes without permission and walking freely here and there when teacher is busy writing lectures on board. Our teacher was a great person she gives us leniency to have a nap for five minutes or talk and ask question anything related to your life or education. But was strict about assignments and essays, she once give us a task to interesting persuasive essay topics. The whole class was least interested to write an essay such a boring thing to do. We all submitted our papers one by one. My teacher was wise she instantly figure out who has copied from the internet and who had done it by themselves. There a software installed in her laptop where she put all the essays and scan it within a second or so. The half of the class was accused of copying the content. They were all failed instantly.