Buzzfeed Editor-In-Chief Ben Smith announced his decision to fire the site's "viral politics" writer Benny Johnson after finding at least "40 instances" of plagiarism in his work on Friday evening in a memo to staff and a post on the site.

"After carefully reviewing more than 500 of Benny’s posts, we have found 41 instances of sentences or phrases copied word for word from other sites," Smith wrote. "Benny is a friend, colleague, and, at his best, a creative force, but we had no choice other than letting him go."

Questions about Johnson's work first came to light after two pseudonymous Twitter users, @blippoblappo and @crushingbort, published a blog post chronicling three instances of plagiarism in Johnson's writing for Buzzfeed.

Smith initially issued a statement to Gawker wherein he defended Johnson as "one of the web’s deeply original writers" and described the issues identified on the blog as "serious failures to properly attribute two quotations and to credit a source." @blippoblappo and @crushingbort subsequently published another blog post identifying several more posts written by Johnson containing content lifted from other sources. After the second post, Smith posted a message on Twitter that said Buzzfeed was "reviewing Benny's work."

Smith's post about the situation on Buzzfeed was entitled "an apology to our readers."

"This plagiarism is a breach of our fundamental responsibility to be honest with you — in this case, about who wrote the words on our site," wrote Smith. "Plagiarism, much less copying unchecked facts from Wikipedia or other sources, is an act of disrespect to the reader. We are deeply embarrassed and sorry to have misled you."

Smith added the site had " corrected the instances of plagiarism, and added an editor’s note to each." On Twitter, Smith refuted suggestions he made the announcement late on Friday evening in order to minimize news coverage. He indicated Buzzfeed staffers began working on the review of Johnson's work Friday morning "and were at the office til 2 am."

"We hardly chose the timing," Smith wrote.

This was not the first time Buzzfeed has faced allegations of taking content from other sources without adequate attribution. In 2012, Gawker and Slate published a pair of articles that described how Buzzfeed writers took ideas and materials from other websites, typically Reddit.

The memo to staff, which was provided to Business Insider by a company spokesperson, was entitled "What we're doing about plagiarism at BuzzFeed." It was co-signed by Smith, Deputy Editor-In-Chief Shani Hilton, Political Editor Katherine Miller, and D.C. Bureau Chief John Stanton.

"Tonight’s decision is not a knee-jerk response to outside criticism, though we are genuinely grateful to the people who helped point out instances of plagiarism. Nor is it meant as a personal condemnation: Benny at his best is a creative force, and we wish him the best," they wrote. "Finally, it is not a warning that you’ll be fired for a small mistake or an isolated error. We will always have a more forgiving attitude toward bold failures, innocent errors, and misfired jokes than more skittish old media organizations. We have more responsibility now than ever now to keep raising our standards and our ambitions, and to continue getting better."

Johnson did not respond to a Facebook message from Business Insider on Saturday morning. A message to his work email address received an automated response that said he was "no longer with BuzzFeed."

Update (12:20 p.m.): Johnson posted an apology of his own on Twitter Saturday morning:

To the writers who were not properly attributed and anyone who ever read my byline, I am sincerely sorry. http://t.co/WpkZIi4g9k — Benny (@bennyjohnson) July 26, 2014

Read Buzzfeed's full memo about Johnson below.