Russia believes that at least 400 Russian Moslems are currently fighting in Syria, out of over a thousand who have gone to Syria so far. Russia is preparing to deal with those who return with lethal intentions. Some of the Russian Moslems fighting in Syria have already made it clear, via videos posted online, that they intend to be as violent back in Russia as they are now in Syria.
In response, Russia recently announced that it was making plans to deal with the Syrian Islamic terrorists who did return to their homes in Russia (largely in the Caucasus, but some are from other Moslem communities in Central Asia, the Crimea, and some major urban areas). Some have already returned, not all of them with lethal intent.
The government preparations were not explained in detail, probably because most of them are generally banned, or at least frowned upon in the West. These forbidden countermeasures include kidnapping, torture, mutilation, and group punishment. That last measure was one of the most effective. If someone was known, or thought, to be an Islamic terrorist, their family could be arrested, tortured, or murdered to change the terrorists mind, or at least discover where he was and arrest or kill him.
The government did announce one obvious measure, that it would arrest any Russian who had returned after fighting with Islamic terrorist rebels in Syria. Based on past performance, the Russians are probably devoting a considerable amount of intelligence effort to finding out who the Russians fighting with the Syrian rebels are and identifying and locating family members of these men who are living in Russia.