Security concerns at the Olympics have dominated headlines over the past month after private contractor G4S failed to recruit the number of guards it had promised. The British government responded by deploying military personnel, and now there are more British troops guarding the streets of London than in Afghanistan.

Martha Crenshaw, a senior fellow at the FSI and CISAC, explains what kinds of threats exist at the Games, the challenges of securing such a large event and whether the failure by G4S will make the Olympics an easier or more attractive target.

What motivates terrorists?

Terrorists want to make a political statement. So you have to ask, "What kind of political statement would attacking the Olympics be?" Al-Qaida could regard the Olympics the way they regard the United Nations. They attacked U.N. headquarters in Iraq and a U.N. agency in Algiers. They regard the U.N. as a tool of the oppressor. That said, they don't talk about the Olympics the way they do about the U.S. – the great Satan, etc. And Muslim countries are competing in the Olympics. Of course they oppose many of the regimes of those countries, like Saudi Arabia.

But I'm not aware of any specific threat to the Olympics or chatter about the Olympics.

Is al-Qaida the only terrorist group to be concerned about?

People will be concerned about Hezbollah now because of the series of foiled attacks against Israel and the successful attack in Bulgaria. Hezbollah and al-Qaida have global reach. But when we talk about al-Qaida, we can't forget the groups affiliated with the main organization: al-Qaida in Iraq and al-Qaida in Yemen, for example. There's also the Pakistani Taliban and other al-Qaida linked groups there.

What kinds of terrorist attacks are of most concern?

We've tended to think, and I stress think, that al-Qaida wants spectaculars. In terms of their attacks in general, targets have often been public transportation. Think of Madrid and London. They're also fond of multiple targets at once, and as regards the U.S., it seems they're still focused on airplanes. We could be dead wrong and they could do something that's totally different but this is the pattern. 

It could be that they'd like a big explosion in the middle of Trafalgar Square, but it wouldn't have to be during the Olympics. There are crowds in Trafalgar Square all the time.  However, if Britain were the target, terrorists might think it's particularly embarrassing and spectacular to attack during the Olympics because it would heighten the fear factor.  On the other hand, it's easier to mount an attack when there is not the high level of Olympics security.

Has there always been a great fear of attacks at Olympics?

The hostage taking in Munich in 1972 (of Israeli athletes) and then the bombing in Atlanta in 1996 have made us afraid that something would happen at the Olympics because it's so prominent.

A recent study concludes that security has been effective. But we don't really know that entirely. We don't know what the terrorists are thinking. We don't know whether they looked at all of the security precautions and said, "This is going to take a lot of work and we will probably fail because security is so good. Let's do something else."

Is London exceptional, because of its size or politics?

From the point of view of this year's Olympics, London could be as much of a target as the Olympics themselves.  But Britain was attacked in 2005 because of their involvement in the war in Iraq, now over. I'm not sure if that changes Britain's vulnerability. We're in the realm of speculation because we don't really know how the adversary is thinking about this. So there is a risk in London but if I were in London I'd be more afraid of a traffic jam.

What does the failure by G4S to provide enough guards say about using private contractors to protect public safety?

Outsourcing security is widespread. A lot of people who were with the military in Iraq and are in Afghanistan are contractors. Everybody contracts out security these days.

But, the question deserves to be looked at. Is it a good idea to rely on these private firms? Would it be a good idea even if all of their people showed up? Are their guards reliable, are they trustworthy, or do they pose a security problem? Have they all been properly vetted to ensure they haven't been infiltrated by al-Qaida and don't include people who are mentally unstable? It raises a lot of questions about who provides security against terrorism for very large international events.

Does the use of military personnel at the last minute create vulnerabilities?

It's possible to imagine that some very determined and nefarious groups would look at this situation and say it's not really going to win us much fame and glory to go shooting a bunch of private security guards, but now the military is a target by being deployed on the streets of London. If someone wanted to attack them, they might think here is the opportunity.

But this switch also means that anybody who decided now that they wanted to target the military or the Olympics won’t have much time to plan. Typically, not always but typically, attacks that cause large numbers of casualties and a lot of destruction have been elaborately planned for a long time – even the lone wolf types like Anders Breivik in Norway or the recent attack in Colorado. Individuals or groups plan in advance and work to get the weapons and explosives, which is not easy. So even if somebody got the idea of doing something it wouldn't be so simple in this short time to come up with a plan and acquire the right materials.

How hard is it to guard a place like London, as well as the Olympics?

It's hard to protect lots of people in a big city. There are lots of crowds, lots of movement. It's not as though you can extend a perimeter; it's a moving target all the time. The Olympics might be a target, London has been a target, so the combination of the two could cancel each other out but I'm sure security officials are worried.

Yet, at this point, if I were the British government dealing with the fallout of the security firm's lack of preparedness, I'd much rather rely on soldiers who have been vetted and have experience than security officers who were quickly brought together.

Brooke Donald is a writer for the Stanford News Service.