This article presents a comparative analysis of online communities of right-wing radicals and Islamists, who are considered to be numerous and dangerous extremist groups in Russian society. The online communities were selected based on the content posted on the largest Russian social networking site VKontakte. The goal of this article is to determine the strategy and tactics employed by extremist online communities for survival on social networking sites. The authors discovered that both right-wing radical and Islamist groups employ similar behavioural techniques, with the mimicry of ideologically neutral content as the most common. In addition, every extremist community also applies some unique methods. For example, if there is a risk of being blocked, right-wing radicals tend to shift their activity and communication to the other Internet-based platforms that are not under state control; however, Islamists prefer to suddenly change the content of their communities (i.e. by using secondary mimicry).