As an editor, I spend a lot of time perfecting punctuation marks and verifying information. Determining where an author’s words end and a quote from another source begins can be one of my most difficult challenges. And yet, protecting an author from claims of plagiarism is one of an editor’s most important tasks.

Last week, as news of Osama bin Laden’s death spread around the world, so did a “quote” from Martin Luther King, Jr.: I will mourn the loss of thousands of precious lives, but I will not rejoice in the death of one, not even an enemy. Returning hate for hate multiplies hate, adding deeper darkness to a night already devoid of stars. Darkness cannot drive out darkness; only light can do that. Hate cannot drive out hate, only love can do that.

I admired the sentiment and, knowing that King had consistently preached nonviolence, I never thought to question its validity. Fortunately, the quote was not in a document I was editing because it was not quite accurate. Others were more skeptical than I was, and a little detective work on the part of some journalists and Facebook users revealed that Jessica Dovey, a Facebook user and middle-school English teacher, first posted the paragraph. Her original post was correctly punctuated to show that the first sentence—I will mourn the loss of thousands of precious lives, but I will not rejoice in the death of one, not even an enemy—was her own. She then added words she admired from King, clearly marking the sentences as a quote. As her post was picked up and passed on, the quote marks and any mention of Dovey were removed, making it look like King had expressed the whole sentiment.

Megan McArdle, business and economics editor for The Atlantic, wrote about the quote, how it started, how it spread, and how the truth behind it was revealed in “Anatomy of a Fake Quotation,” http://www.theatlantic.com/national/archive/2011/05/anatomy-of-a-fake-quotation/238257/. It is a fascinating look at how the partially misattributed quote was created by the relaxed rules and abbreviated formats of Twitter and Facebook and then disseminated through those media more quickly and widely than would have been fathomable even five years ago.

If you’re an editor, it’s a very scary story.