Yes, he had shared notes with friends in the course. But the instructions on the exam said students should consider it “completely open book, open note, open Internet, etc.” The professor had encouraged students to collaborate in their other course work. So even though the exam also included the admonition that “students may not discuss the exam with others — this includes resident tutors, writing centers, etc.,” the student said he figured it would be safe to swap a few ideas.

Besides, he knew something about tests. He had worked as a teaching assistant himself, helping another Harvard professor administer exams.

“My understanding was that you shouldn’t sit down and take a test with someone else, or take someone else’s test and present it as your own,” he said. “But I wrote my own answers on the final.”

In May, he graduated cum laude, settled into a job, and thought no more about “Intro to Congress” until early August, when the e-mail from Harvard’s Administrative Board came. He read as far as “may have an impact on your degree” before he got angry, then worried: What was he going to tell his new boss?

Dozens of Harvard students are in similar positions after Thursday’s announcement that about 125 of them — almost half of the 279-student “Intro to Congress” roster — are suspected of cheating on the course’s final exam. In May, a teaching fellow noticed suspicious similarities among many of the test answers and notified the professor.

Some students admit to sharing ideas and source material during the week they were allotted to finish the exam. But all of those interviewed by the Globe — who requested anonymity because they feared the consequences of going public while their cases are pending — said the ground rules for both the test and the class at large were so unclear that they did not realize they were cheating.

That may partly answer the question on the minds of many at Harvard since Thursday: How could this have happened?

Some, such as the prominent education professor Howard Gardner, believe the episode is a sign of “the regular thinning of ethical muscles in our country.”

“If for 20 years you’ve been studying young people, this isn’t surprising,” he added. “In many ways they’re lovable and inspiring, but they cut corners the way you would jaywalk. . . . This is a textbook example of people doing what they think they can get away with rather than what they should be doing.”

Other faculty members said they believe take-home exams entail too much temptation. On blogs and in interviews Friday, Harvard professors raised a cry: bring back the in-class final.

Still others said it might be time for Harvard to break with nearly 376 years of tradition and institute an honor code. Such policies are surprisingly rare at elite schools.

The idea gained momentum at Harvard two years ago, when a new academic integrity committee started considering ways to combat plagiarism, a phenomenon made too easy by the Internet and all too common by a generation that has grown up with shifting norms about the meaning of authorship.

But many at Harvard may resist an honor code, which was roundly rejected by a 1985 college committee. Some note that there are conflicting data on whether the codes work.

“I do think more understanding [of academic ethics] would be helpful,” said Michael Mitzenmacher, a Harvard computer science professor who has served on the college’s Administrative Board, the body that oversees disciplinary issues. “But I don’t think a stated honor code necessarily would be.”

Before Harvard administrators can make any long-term decisions following the cheating scandal, they will have to decide what to do with the 125 or so students scheduled to appear before the Administrative Board in the next few weeks. Penalties could range from mild admonitions to yearlong suspensions.

The deliberations will not be easy, given the apparent complexities of the scandal.

Matthew Platt, the professor in question, did not respond to several requests for comment.

But one accused student said all the “et ceteras” in the exam instructions may have left people confused: “It was blurry, it was murky.”

Only half-joking, he added: “If I posted my exam answers on the Internet and you found them, could you then use my exam as a source?”