Ayman al-Zawahri, Osama bin Laden's number 2 has taken up the reins of al-Qaeda following the death of its former leader. Born in 1951 into a wealthy Cairo family, he had for long been seen as the real brains and organiser of al-Qaeda even before bin Laden's death.

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When terror groups get organised: this Al-Shabaab troop show the danger of failed states. They not only provide a vacuum where fundamentalist groups face no prosecution, they also provide a training base for these groups.

© Reuters Feisal Omar

'If you look at the millions of people killed in criminal enterprise, they are numbers that terrorists can only dream of.' Misha Glenny, author of McMafia, outlined to NATO Review how organised crime activities regularly kill far more people, but far less spectacularly, than terrorism.

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Home grown terrorism - with a twist. In London, on July 7, 2005, four Englishmen blew themselves up on public transport in the heart of the city. Though designed as a protest against the actions of the UK, they succeeded in killing people from around the world, including fellow Muslims.

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'Lone wolf' terrorist attacks took on a shocking new face in 2011. Anders Behring Breivik attacked through bombs and bullets. He attacked both young and old. And he shook deeply the idea that terrorism doesn't happen in stable, peaceful countries.

© Reuters Fabrizio Bensch

On the battlefield, Afghanistan saw the rise and bloody success of the IED (improvised explosive device). The Taliban, realising that they could never win symmetric battles, switched to a tactic which kills indiscriminately. The biggest killer of both Afghan civilians and foreign soldiers in Afghanistan remains the IED.

© Reuters Yannis Behrakis

The threat of terror can be almost as potent as the act. North Korea's leader Kim Jong-Il knows it too. By developing a nuclear weapon, carrying out nuclear tests and making bellicose statements, he knows that he can use the threat as a bargaining chip for his impoverished nation.

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Knowledge is power: the most famous peddler of nuclear secrets was A. Q. Khan. The knowledge he passed on was not the only threat. It was also that it became clear that the knowledge was easy to access and there were many willing buyers actively looking for it.

A massive attack can now be cheap, quick and difficult to prevent. Cyber attacks such as distributed denial of service (DDOS) attacks can be done even by unwitting computers which have been taken over. Despite being simple attacks, they can have a major disruptive effect on key institutions.

The oldest security threat of all? Piracy has seen a sad resurgence in the first decade of this century. While the end of the last century saw a major reduction of piracy in the Straits of Malacca, this century has seen its almost exponential rise off the horn of Africa.

© Reuters Ho New

Not all terrorist activities can be stopped. But life can be made difficult for them. NATO's Operation Active Endeavour has been designed for the last 10 years to make sure that the Mediterranean Sea is a no-go area for terrorists.

© Reuters Christian Charisius

Terror can be stretched over long periods. In Colonel Qadhafi's case in Libya, over 42 years. His regime not only funded terrorism abroad, but also regularly terrorised his own people. This continued right up to its final days. But then came the relief.

© Reuters Louafi Larbi