Although this is written for the younger student the concepts of "visible thinking" in online education are phenomenal. form, function, connection and reflection
This article compares the work patterns of a more successful and a less successful online group collaboration and draws conclusions about strategies that instructors can promote/encourage/require to help students successfully collaborate.
If a group worked together to cheat, that certainly would be successful collaboration. I'm sure there are articles out there (that I haven't come across yet) that discuss strategies to minimize or circumvent cheating. Scaffolding assignments and requiring students to make visible all the steps in the process would help I think. Thanks!