One of the Top 10 CS universities I studied at had some system for that, obviously it couldn't catch somebody who was a good programmer and could reshuffle AST

One of the Top 10 CS universities I studied at had some system for that, obviously it couldn't catch somebody who was a good programmer and could reshuffle AST with properly renamed variables. But it was still helpful for less-gifted students who cheated. Typically teachers had to set a threshold of similarity for their given assignments over which it was automatically reporting student names. The software scrapped GitHub as well.