The goal of this study is to identify the problems in the existing system of criminological prevention of extremist crimes committed using information and telecommunication networks, and to work out ideas for its improvement. The authors use general and special research methods, primarily, sociological ones. They have studied 184 criminal cases of extremist crimes committed using information and telecommunication networks tried in courts in the cities of Irkutsk, Moscow, Penza, in Kursk, Moscow, Murmansk, Samara and Chelyabinsk Regions and in the Republic of Bashkortostan in 2010–2017. The have also analyzed the published decisions of the Supreme Court of the Russian Federation and surveyed 158 employees of the internal affairs bodies, 42 judges, 80 employees of the Investigation Committee of the Russian Federation, as well as 46 faculty members from Moscow, Moscow Region and the Republic of Bashkortostan. The authors have analyzed statistical data for 2010–2017 gathered by the Chief Information and Analytics Center of the Ministry of Internal Affairs of Russia and the Court Department of the Supreme Court of the Russian Federation. The article takes into account novels of criminal legislation regarding the use of information and telecommunication networks for committing extremist crimes introduced in 2013–2017, the clauses of the Federal Law «On the Basics of the System of Preventing Crimes in the Russian Federation» of 2016. The authors also pay attention to the Strategy of State National Policy of the Russian Federation until 2025, the Counter-Extremism Strategy of the Russian Federation until 2025, the Doctrine of Information Security of 2016, the Strategy of Developing Information Society in the Russian Federation in 2017–2030, and the new Clarifications of the Plenary Session of the Supreme Court of the Russian Federation. A complex research of the problems of counteracting extremist crimes committed with the use of information and telecommunication networks allowed the authors to formulate suggestions on improving the system of criminological prevention of these criminal acts.