Computers are a great invention, but they have one big downside: They make plagiarism a simple matter of clicking on “copy” and “paste.” High school and college students know this. Their teachers know it. Even newspaper and magazine writers know it. And famous authors like Stephen Ambrose and Doris Kearns Goodwin know it, to their shame and humiliation.

High schools and colleges find themselves in the midst of an epidemic of plagiarism. Students lift whole paragraphs from reference sources or copy entire term papers off Internet services, passing such material off as their own work. But teachers now can use computer programs to compare suspicious passages in student papers against a wide range of source materials. This sleuthing often turns up similarities that point to plagiarism.

Harsh punishment can be the result. Many schools have adopted a “zero-tolerance” policy, accepting no excuses for copying without attribution. Although some educators are more forgiving, at least for a first offense, many will give no credit for an offending paper or even flunk the offending student. Getting no credit for a term paper, even getting flunked out, are tough punishments for a misdeed that has become as easy and commonplace as running a red light or drinking an illegal beer.

But think how tough it is for a famous author such as Stephen Ambrose to be dropped from some college reading lists after word sleuths found many close similarities between his recent best-seller about World War II aviators, “The Wild Blue,” and Professor Thomas Childers’ 1995 book, “Wings of Morning.”

Ms. Goodwin had still more to lose. The long-respected and prolific historical commentator has suffered cancellation of lecture dates, withdrawal from this year’s proceedings of the Pulitzer Prize board, and forced leave of absence from “The NewsHour with Jim Lehrer.” All this because an anonymous informant reported that her 1987 best-seller, “The Fitzgeralds and the Kennedys,” contained passages identical with Lynne McTaggart’s earlier book, “Kathleen Kennedy: Her Life and Times.” Ms. McTaggart spotted the copyright infringements (footnoted but not enclosed in quotation marks). She sued. Her publisher quietly settled the case for around $50,000. Ms. Goodwin apologized, explained that she had confused notes from the McTaggart book with her own notes, revised her book for another edition, and tightened up her research methods.

Case closed? Not by a long shot. Mainstream newspapers and talk show hosts, sensing a juicy scandal, speculated that Ms. Goodwin’s later books, including her Pulitzer Prize-winning “No Ordinary Time,” may also have involved plagiarism. The New York Times published a supposedly humorous satire speculating without foundation that she had lifted passages from Roger Kahn’s “The Boys of Summer” for her new memoir, “Wait Till Next Year.” (The Times later published two editor’s notes clarifying the satire lest readers accept it as factual.) And several accusers found fault with Ms. Goodwin’s efforts to explain and defend herself.

To the rescue has come The Wall Street Journal’s Dorothy Rabinowitz, a tough, clever, Pulitzer Prize-winning writer who often dares to differ from the Journal’s conservative editorial page. Ms. Rabinowitz says some people “know exactly how possible it is to do such things when writing in haste, and a certain passion.” As for Ms. Goodwin’s explaining her case, “Where would she go to get her situation resolved? Is there some central office for penitents where she could earn certificates of resolution?” Yet, “the stories roll on about a payoff, as though no one reputable had ever settled a case. Ms. Goodwin, of course, has by now paid more than she could have dreamed.”

The lessons are clear: Don’t copy other people’s work and pass it off as your own. If you get caught, apologize and change your ways. And after you have reformed, hope that you have a tiger like Dorothy Rabinowitz on your side.