Although there are plenty of candidates for this title, the most pernicious item that has ever appeared on the Internet may be Inspire, the online English-language magazine circulated by al Qaeda. Part of its goal is to instruct individual would-be jihadis how to cause the maximum carnage without access to modern arms or explosives.

Why not just drive a car into a crowd of infidels? Or build a bomb from a simple pressure cooker? And as the British Daily Telegraph was the first to point out, the bomb design offered by the magazine was precisely that adopted by the Tsarnaev brothers in their deadly attack in Boston. The mere fact of borrowing a technique proves nothing about ideology, but the brothers' actions so precisely fit those of dozens of other lone wolf terrorists in the West in recent years that it is virtually certain that they were following the al Qaeda playbook.

In itself, the idea of Chechen extremists identifying with al Qaeda is hardly surprising, as the movement has for twenty years made the Caucasus region one of its principal battlefronts worldwide. From a historical perspective, though, that alliance should give us pause. Muslims in these parts have a very long tradition of religious-based insurgency directed against the Russian state, dating back almost two centuries. For most of that time, resistance stemmed from one particular tradition within Islam, namely the Sufi mystical brotherhoods. The Sufis, though, are anathema to the stringent fundamentalist version of Islam preached by al Qaeda. In Pakistan and Iraq especially, al Qaeda followers regularly target Sufi shrines and devotees for terrorist violence.

While Westerners tend to lump all forms of Islamic-inspired violence under a common jihadi label, Chechen-related militancy involves some truly odd and counter-intuitive alliances. Ideally, that internal conflict should give non-Islamic states some leverage in discouraging the spread of al Qaeda militancy.

Scarcely had Tsarist Russia established control in Caucasian regions of Chechnya and Dagestan than local Muslims began their campaigns of resistance. From 1830 through 1859, the Russians faced a deadly guerrilla war led by folk-hero Imam Shamil. Beyond being an Islamic leader, Shamil was also a leader of the Naqshbandi school of Sufi Islam, which still flourishes across Central Asia and much of the former Soviet Union. Then and since, such secretive brotherhoods provided a wonderful institutional framework for clandestine organization.

The Russians acknowledged the central role of the brotherhoods by the names they gave their rebel opponents. Tsarist officials called them muridists, from murid, a Sufi disciple. The Soviets later denounced their enemies as zikristi, those who repeatedly chanted the dhikr declaration of faith in order to bring themselves into an ecstatic state. But whether murids or zikrists, there was no doubt about the Sufi foundations of Chechen nationalism, which time and again sprung to life to challenge Russian rule. In 1944, the sheer impossibility of suppressing zikristi persuaded Stalin to deport most of the Chechen people to Central Asia, where they remained until 1957.

Islamic pride and self-awareness revived during the 1980s, as the Soviet Union lurched towards dissolution. We get a hint of this, oddly, from the names of the two Tsarnaev brothers themselves. Tamerlan, born in 1986, was named for the great Islamic conqueror of the fifteenth century, Timur or "Tamerlane." Dzhokhar, born 1994, received the name of Dzhokhar Dudaev, the first president of the breakaway Chechen republic, and a hero of Islamic nationalism.

Sporadically from 1994 through 2009, the Russians found themselves repeatedly at war with Chechens and neighboring Caucasian peoples. Giving a sense of historical déjà vu, insurgents based themselves explicitly on the old Sufi heroes. Their most ferocious commander -- and a persistent sponsor of vicious acts of terror -- was Shamil Basayev, who took his name from the nineteenth century imam.

From the mid-1990s though, the region's endemic violence drew in a new religious and military force, namely the newly formed al Qaeda. Saudi militant Emir Ibn al-Khattab brought thousands of foreign fighters to assist the Chechen war effort, many trained in Afghanistan and Pakistan. In fact, several of the later 9/11 hijackers originally joined the global jihad specifically to fight Russians in the Caucasus, and only later were they redirected against the US mainland. Osama bin Laden's second in command, Ayman al-Zawahiri, made a personal visit to try and create an al Qaeda base in Chechnya. The horrific recruitment videos circulated online by al Qaeda propagandists often show the murder and beheading of Russian soldiers.

As I have suggested, the religious slant of al Qaeda was radically hostile to Sufi traditions. Their own background was Wahhabi or Salafist, and condemned the Sufi brotherhoods as semi-pagan, both for their mystical practices and their devotion to saints and local shrines. Despite this, their fanatical militancy gave al Qaeda's foreign fighters enormous prestige in the North Caucasus, where networks of Islamist militia soon developed. In turn, al Qaeda tactics influenced the older local movements. Chechen militants now launched terror attacks aimed at inflicting mass civilian casualties, and increasingly used suicide bombers -- including women. Ibn al-Khattab himself formed a close personal relationship with Shamil Basayev.

Yet the Sufi heritage has not vanished, and Chechen Muslims are usually much more broad-minded in their religious practice than the puritanical Wahhabis. While Chechens definitely want an independent Islamic state, few wish to live in a Caucasus emirate under stringent Sharia law. That outlook has translated into politics. While early Chechen leaders were religiously moderate, their successors have had to become more ostentatiously pious and Muslim -- but they do so in a way that is strongly Sufi.

Since 2007, the Chechen head of state has been Ramzan Kadyrov, who has vigorously promoted Sufi Islam as a deliberate counter-balance to alien Salafi influences. He is himself a disciple, a murid, of the Qadiriyya order, and regularly holds dhikr ceremonies. In public life, his administration has built and rebuilt mosques, including most sensationally a pilgrimage shrine (a ziyarat) commemorating the nineteenth century sheikh Haji Kunta. At a time of war and devastation in Chechnya, Kunta was a famous mystic who led a Sufi revival, and became so venerated as to gain supernatural status: for his devotees at least, he never died. He thus represents everything the Wahhabis and al Qaeda loathe in the practice of Islam, and militants regularly threaten Kadyrov's life. Presently, though, the state-sponsored Sufi revival shows no obvious signs of abating.

Not just in Chechnya, Sufi Islam remains an enormous obstacle to al Qaeda and its supporters. Treated with due caution and respect, it could yet become a potent de facto ally for Western interests.