"CS is different, because the capacity for copying is so large," he says.
And although paper mills on the Internet are selling essays and reports to college students all over the country, Lewis says the current system works fine.
"I'm not aware of anyone doing anything systematic," he says. "In some cases, cheating is easily detected-- the [plagiarized] work is either of a distinctive style or of horrible quality. People notice these things."
And Lewis says CS classes vary in the amount of collaboration they permit. In his own class, for instance, students are allowed to collaborate in small groups, as long as the written work they submit is original.
"In fields like computer science and engineering, in the real world, collaboration is good," he says.
--Joyce K. McIntyre contributed to the reporting of this story.