Editors at CNN were performing a regular spot check of content in the organization's publishing queue last week when they discovered that a story by London bureau news editor Marie-Louise Gumuchian included material taken without attribution from another source.

Using plagiarism detection software, they quickly turned up more examples and in the end have so far found that Gumuchian plagiarized in roughly 50 articles.

CNN leadership announced their findings and her firing in an Editor's Note published today. Gumuchian was on the CNN world desk, and appears to have written frequently about the Middle East, among other topics.

"Most of what we found was [lifted] from Reuters, which she was previously employed by," says a CNN source who asked not to be identified due to the fact that they were not cleared to speak publicly about the incident. "We also notified [Reuters]. She worked for us for about six months, so if we found that many in six months I can't imagine the job Reuters has now."

Reuters is reviewing Gamuchian's work, a spokesman told Poynter. She worked for Reuters for roughly nine years, according to the CNN source.

"It's kind of ballsy — don't you think your old colleagues might look to see what you were doing at your new job?" the source said, adding that as a longtime journalist it's unlikely Gumuchian thought it was okay for her to use Reuters wire content without attribution. Or that it would be acceptable.

The editor's note about Gumuchian said CNN has gone in and "removed the instances of plagiarism found in her pieces. In some cases, we've chosen to delete an entire article." That's happened in seven instances, the source said.

Articles that were updated include a note informing readers of the reason for changes. Here's an example:

Editors' Note: This article has been edited to remove plagiarized content after CNN discovered multiple instances of plagiarism by Marie-Louise Gumuchian, a former CNN news editor.

CNN has also sent a note out to all CNN wire clients to inform them of the offending articles, so they could add any editors' notes as needed.

As for the deleted stories, the source said this was done "because the plagiarism was so extensive ... we killed the whole article because it was so blatant." Here's the text that appears at deleted story URLs:

(CNN) -- This article has been removed after CNN discovered multiple instances of plagiarism in this story.

I asked if readers going to the URL of the removed article will see some kind of note explaining why the article has disappeared, and the source wasn't sure if that was being done or not. (I'll update with any news on that issue.)

The source said spot checks for attribution and plagiarism are a regular part of CNN's editorial workflow. "She only worked for us for six months and we identified it."

It's encouraging that CNN caught her so soon into her tenure. However, by that time she had already caused a lot of damage. Perhaps the spot checks need to be increased, given the amount of content being produced. I also hope CNN moves the editor's notes from the bottom of the offending articles up to the top.

If you're wondering about best practices for handling an incident of plagiarism or fabrication, Kelly McBride and I previous offered a comprehensive guide.