From NPR reporter David Folkenflick's "Murdoch's World," as quoted by Media Matters:
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.
Folkenflik explained in the book's endnotes that four former Fox News employees described the commenting practice to him, according to Media Matters.