During the decades of the Cold War Russia armed itself for an eventual attack from the outside. Today the threat to Russia's security and stability comes not from the outside, but from within, in the form of radical, militant Islam.

The threat of terrorist attacks by fanatical Islamists against Russian cities is as real as the threat against cities in the United States or in Western Europe.

The danger for Russia is all the more real given that it has large Muslim populations that are part of the Russian Federation, such as Chechnya and Ingushetia.

Russian troops have in the past engaged in fierce fighting with Muslim separatists causing many deaths and much destruction in those autonomous regions. And the rebels have hit back through terror tactics and suicide bombings.

But if Russia has opened up one aspect of its previously closed society, modernizing business and doing away with communism in favor of a free market economy, in the murky world of terrorism and counter-espionage not much has changed over the years as Moscow tries to keep a lid on much of what is going on in its dealings with Islamist terrorists.

How serious should the world, and indeed Russia itself, take the Muslim terrorism threat? Very seriously says Gordon M. Hahn in his book, "Russia's Islamic Threat," and in which he outlines five reasons.

First, there is always the real danger that an Islamic network in Russia could work in favor of the international Islamist movement by providing them resources in men and support.

Second, with the backing of the al-Qaida franchise or some other pan-Islamic movement a jihadi movement in Russia, according to the author of the book, might destabilize or instigate civil wars in parts of the federation.

Third, if some of the autonomous Muslim republics manage to secede from the Russian Federation and establish themselves as caliphates, that could pave the way for Osama bin Laden's dream – the establishment of a wider caliphate encompassing all the Muslim lands from Afghanistan to China in the east and from the former Soviet republics into Europe and beyond.

Fourth, the acquisition by radical Islamists of weapons of mass destruction with which they could use to threaten other states.

And fifth, a campaign to destabilize Russia by Islamists could result in the central government in Moscow resorting to extreme measures which would only serve to further empower the Islamists.

But all is not gloom and doom. The author offers a number of well thought out ideas such as greater cooperation between Western and Russian intelligence services, promoting greater understanding between different cultures and Russia, and encouraging the moderate branch of Islam to play a more active role.

The difficulty, as always, will be to get the silent majority to speak up.