According to HuffPo, the cheating occurred on a take-home final exam; Harvard isn't saying the name of the course, but  at least 250 students were enrolled, and about half of said students are under investigation for possible cheating. From HuffPo's conversation with dean of undergraduate education Jay M. Harris:

A teaching assistant noticed some possible problems on the tests, including evidence that students collaborated on answers or used the same long, identical strings of words. The exam had clear instructions that no collaboration was allowed, Harris said.

The assistant notified the professor, who referred the case in May to the administrative board. After interviewing some students, the board found what Harris characterized as "cause for concern."

While the investigation is ongoing, punishments could range from formal admonitions to forcing students to withdraw from the university for one year, HuffPo says. If you caught our story on this summer's string of cheating scandals, you know which end of the spectrum we guess the penalties will fall on.