Despite an apparent upsurge of terrorism, including the attack on President Karzai of Afghanistan, a return of suicide bombings in Iraq and a spate of assassinations in Lebanon and North Africa, in the Muslim heartlands al-Qaeda is on the retreat. The call on devout Muslims to purge the Islamic world of its corrupt rulers, that fell on such fertile ground in the Arabian peninsula, is losing its pull. In Saudi Arabia, a police crackdown and the arrest and re-education of scores of extremist preachers have persuaded thousands to renounce their former loyalty to Osama bin Laden. In Iraq, the targeting of civilians by suicide bombers and al-Qaeda's torture of sectarian enemies has so sickened tribal leaders that most are joining in the fight against foreign extremists. And in North Africa, security forces have recently killed some 20 suspected militants.

The virulent ideology, spawned by anger at Western troops in Saudi Arabia and the perceived corruption of ruling elites, has, according to senior intelligence officers, been dissipated as terrorist groups increasingly become a front for drug smuggling, extortion, crime or ethnic hatred. Frustrated zealots have seen their attempts to rid Muslim societies of Western influence mocked and thwarted. Moderates have spoken out, Governments across the Middle East have woken up to the threat and nowhere has crude Islamism triumphed. Another spectacular atrocity remains a possibility, but the core ideology has less traction across the Muslim world.

Al-Qaeda, however, is far from beaten. Its figurehead leadership remains at large somewhere in Pakistan's tribal areas, issuing regular new calls for jihad against the West. Its amorphous and shadowy structure serves as a cover for any terrorist franchise pledging support for its nihilistic aims. And on the fringes it has seen new successes: the emergence of an umbrella group in North Africa, al-Qaeda in the Land of Islamic Maghreb, that has subsumed the more virulent Algerian and Moroccan Islamist movements and linked them specifically with the al-Qaeda name and aims. In Somalia, the Islamic Courts movement, that briefly held sway during the power vacuum in Mogadishu, has seen a resurgence of support as age-old antagonism to neighbouring Ethiopia pits the Islamists as champions of resistance to the US-backed Ethiopian incursion. And though an al-Qaeda military leader and bin Laden associate was reported killed there yesterday in a US attack, the Islamists are now well-entrenched and able to fight a long guerrilla war.

Westerners and Western values remain the target. In North Africa tourists have been murdered and kidnapped, a United Nations compound has been bombed, and militants have been trained at desert camps with plans to infiltrate Europe. Youths as young as 15 are being recruited as networks are pushing south. The richest prize is Nigeria: if tribal tensions can be exploited, the Muslim north radicalised and Nigerian Islamists trained as sleepers to be activated in Britain and other European countries, Western intelligence could face a massive new threat on its doorstep.

Al-Qaeda remains a danger, but there is now a real chance that this backward-looking ideology can be defeated. Global terrorism is still a serious threat and parts of al-Qaeda's deadly virus may mutate. The West must remain vigilant to confront these mutations wherever they appear.