Confronted by charges of plagiarism, BuzzFeed on Friday fired Benny Johnson, the viral politics editor whose work often typified the website's energetic storytelling style.

BuzzFeed editor in chief Ben Smith said he and his colleagues had identified "41 instances of sentences or phrases copied, word for word, from other sites, many of them inappropriate sources in the first place," during a review of about 500 posts by Johnson.

"This pattern is not a minor slip," Smith wrote in a memorandum to BuzzFeed staff on Friday night. "This is a breach of faith with our readers; a violation of a basic rule of writing; and the reflection of an unserious attitude to our work that is wildly out of line with both our standards and our ambition."

Smith also published an editors' note that apologized to readers. He said corrections had been made to each of the 41 posts where plagiarism and attribution issues were found.

Many of the posts consisted of creative lists ("The 17 Best Swag Gifts Obama Has Received From Foreign Leaders") and regurgitated content from other sources ("FDR Had The Greatest Childhood Ever"). One image-heavy post, "The Story Of Egypt's Revolution In 'Jurassic Park' Gifs," plagiarized wording from Wikipedia; another, "7 Things Democrats Would Have Freaked Out About If Bush Had Done Them," copied phrasing from The Hill newspaper.

On Saturday morning, Johnson wrote on Twitter, "To the writers who were not properly attributed and anyone who ever read my byline, I am sincerely sorry." He then shared a link to Smith's editors note.

As websites grow up, their standards go up. And Smith, who was hired at the end of 2011 to turn the viral site into a bonafide news source, acknowledged as much in his editors' note.

"BuzzFeed started seven years ago as a laboratory for content," Smith wrote. "Our writers didn't have journalistic backgrounds and weren't held to traditional journalistic standards, because we weren't doing journalism. But that started changing a long time ago."

He cited the "high standards" of BuzzFeed's journalists and the "increasingly careful attribution" practices of "the people who produce our immensely popular entertainment."

For years, BuzzFeed has been scrutinized for its attribution practices, since some of its most popular material originates on Reddit and other social networks.

Partly thanks to its aggressive aggregation techniques, the venture capital-backed website has grown incredibly quickly; it now has 150 million unique visitors a month around the world. A story that emerges on Reddit one day can be picked up by BuzzFeed the next day and make it onto a network morning show or CNN the next.

Nowadays, though, BuzzFeed also breaks news stories on its own, and those exclusives live right alongside sponsored posts from advertisers and lists like "29 Essentials For Throwing The Perfect 'Harry Potter' Party."

The decision to dismiss Johnson is likely to trigger more scrutiny of the site's practices.

Accusations of plagiarism by Johnson first surfaced online on Wednesday. When Gawker wrote about several examples of copied language on Thursday, Smith called them "serious failures," but also expressed support for Johnson, calling him "one of the web's deeply original writers, as is clear from his body of work."

After Friday's more thorough review of Johnson's work by BuzzFeed editors, however, Smith said, "We had no choice other than letting him go."

Matthew Ingram, a GigaOm senior writer who closely follows digital journalism, commented on Twitter that BuzzFeed's apology felt "like a stake in the ground, showing they are serious about getting serious."

In Smith's more detailed memo to his staff on Friday night (which was provided by a BuzzFeed spokeswoman), he said BuzzFeed would change its orientation procedures for new employees to "make sure that the high standards of training that come with our fellowship program extend to everyone who arrives at BuzzFeed -- and particularly to those without a background in traditional journalism."

He concluded his memo by saying, "We have more responsibility now than ever now to keep raising our standards and our ambitions, and to continue getting better."