20 years ago (so very outdated), I TAed an introductory CS class for engineers who weren't going to be majoring in CS. We used MOSS [1]. Maybe it was the threshold we picked, but the results were pretty blatant. People renamed variables, renamed functions, changed comments, and the clever ones inlined or extracted a function. A lot forgot something, copying a bug or quirk from the original.

[1] https://theory.stanford.edu/~aiken/moss/