At university, my degree had this mandatory software engineering course for which there was a group assignment. You had to pick a project and "implement" it as a group. You weren't expected to write any code though - only produce a requirements spec, design spec, project plan, UML diagrams, etc – the group was marked on those specs/plans. You had to choose a software development methodology and justify why it was the right choice for your project.

The lecturer told us very clearly "DO NOT LOOK AT PREVIOUS YEARS ASSIGNMENTS". I was a little naughty, I asked a friend who did it the year before if I could have her group's assignment to read, because they'd got near-perfect marks. I didn't copy anything from it, I just read it to get a better idea of what was expected.

One guy in our group, he was really late to contribute his section of the assignment. When he finally gave it to me to read, I realised he'd just copied my friend's assignment from the previous year – either she'd given it to him also, or someone else in her group had. He tried to cover up his copying by rewording sentences, but it was very obvious – every paragraph made the same points in the same order, using the same (or very similar) word choices. Added to that, a lot of his attempts to reword it, the end result didn't even make much sense – some sentences, all he'd done was transform good grammar into bad.

I was angry and felt like reporting him. But, the only way I knew he was cheating was because I'd looked at a previous group's assignment, against explicit instructions not to – I couldn't see a way to get him in trouble without getting myself in trouble. In hindsight, I probably could have shown it to my friend and then got her to claim she'd spotted the plagiarism instead of me, but I didn't think of that at the time. Instead I just threw it out and redid it from scratch myself. He got the same marks as everyone else on the group assignment, without having contributed anything except a poor attempt at plagiarism.