The EU also proposed (and implemented?) its own online propaganda army long before Brexit, so the Russians might not be the only ones to interfere in public opinion.
"In order to reverse the perception that 'Europe is the problem', we need to communicate that the answer to existing challenges... is 'more Europe' not 'less Europe'."[1]
[1] http://www.telegraph.co.uk/news/worldnews/europe/eu/9845442/...