NPR media reporter David Folkenflik writes in his forthcoming book Murdoch's World that Fox News' public relations staffers used an elaborate series of dummy accounts to fill the comments sections of critical blog posts with pro-Fox arguments.

In a chapter focusing on how Fox utilized its notoriously ruthless public relations department in the mid-to-late 00's, Folkenflik reports that Fox's PR staffers would “post pro-Fox rants” in the comments sections of “negative and even neutral” blog posts written about the network. According to Folkenflik, the staffers used various tactics to cover their tracks, including setting up wireless broadband connections that “could not be traced back” to the network. 

A former staffer told Folkenflik that they had personally used “one hundred” fake accounts to plant Fox-friendly commentary:

On the blogs, the fight was particularly fierce. Fox PR staffers were expected to counter not just negative and even neutral blog postings but the anti-Fox comments beneath them. One former staffer recalled using twenty different aliases to post pro-Fox rants. Another had one hundred. Several employees had to acquire a cell phone thumb drive to provide a wireless broadband connection that could not be traced back to a Fox News or News Corp account. Another used an AOL dial-up connection, even in the age of widespread broadband access, on the rationale it would be harder to pinpoint its origins. Old laptops were distributed for these cyber operations. Even blogs with minor followings were reviewed to ensure no claim went unchecked.  [Murdoch's World, pg. 67] 

In the book's endnotes, Folkenflik explains that “four former Fox News employees told me of these practices.” It's unclear whether these tactics are ongoing.