Re: Manipulating 'most popular'
Facebook's "trending" is as bad. When the Costa Concordia was righted all the new stories kept mentioning that it was actually bigger than the Titanic. So Facebook decided that the Titanic was a trending story.
Companies buy likes and pay for positive comments for their stuff and some pay for negative comments on rival products.
Going from that sort of stuff GCHQ "manipulating" stuff like that isn't exactly unexpected.