On Sunday the New York Times quoted "law enforcement sources" as saying that she had made postings on her stream. The story got a huge amount of coverage and even came up during Tuesday's Republican debate.
On Wednesday, FBI Director Comey described the reporting as "grabled" and clarified that no, it was just private messages -- and the Times (and others) rewrote their stories to reflect it. But you can't unring a bell; most people's opinion, and even more importantly their emotional responses, are based on the original story.
Erik Wemple covers this well in the Washington Post [1]
Times' "public editor" Margeret Sullivan's looks at it as well [2], noting that two of the reporters also incorrectly reported that Hillary Clinton was the target of a criminal investigation.
[1] https://www.washingtonpost.com/blogs/erik-wemple/wp/2015/12/...
[2] http://publiceditor.blogs.nytimes.com/2015/12/18/new-york-ti...