LOS ANGELES, August 28, 2011 (AFP) - The 9/11 attacks spawned a huge, lucrative market for security, but experts say the sector must adapt as Americans do not feel as threatened as before, especially after the killing of Osama bin Laden.

Ten years after the strikes that killed nearly 3,000 people on American soil, security and counter-terrorism businesses will have to look to the future and develop new technologies to combat new threats, they say.

"Saying that private security has been growing after 9/11 is an understatement," counter-terrorism expert Eroll Southers, who is a professor at the University of Southern California, told AFP.

"I believe that Osama bin Laden created an industry. He has, with the attacks of 9/11, created an environment which will never again allow us to do things that we did before that attack."

The security and counterterrorism market is diverse, including everything from surveillance and private security to consulting, technology development, training. Clients range from individuals to multinationals and governments.

Michael Intriligator, a professor of public policy at the University of California (Los Angeles), explained the business was an "evolving" one.

"It was a very small market before 9/11 and it's growing into a large market. We are talking about billions of dollars," Intriligator told AFP.

"People want security and are willing to pay for it; electronic devices, sensors, guards, et cetera," he added.

"The challenge is immense, because there are so many points of vulnerability in this country. We have an immense number of targets."

But Ohio State University professor John Mueller argued in The Los Angeles Times that the burgeoning security industry -- estimated to swell in the United States to $31 billion by 2014 -- relies heavily on overblown risk.

"The number of people worldwide who are killed by Muslim-type terrorists, Al-Qaeda wannabes, is maybe a few hundred outside of war zones. It's basically the same number of people who die drowning in the bathtub each year," he said. "So if your chance of being killed by a terrorist in the United States is 1 in 3.5 million, the question is, how much do you want to spend to get that down to 1 in 4.5 million?"

According to the 2010 annual report of Sweden's Securitas, a world leader in private security and the number one firm in the business in the United States, just seven firms share 52 percent of the US market.

Last year, Securitas posted turnover of $3.6 billion in North America.

"We have seen companies over the years that moved into this industry that had no interest in this industry a year ago, understanding how lucrative it is. It is never going to go away," Southers said.

"This is a very wise investment if you're a technology developer."

The security sector however was not immune to the global financial crisis. Despite posting big numbers, Securitas nevertheless saw its turnover fall four percent between 2008 and 2009, and an additional two percent the next year.

For terrorism expert Jeffrey Simon, a professor at UCLA and author of "The Terrorist Trap: America's Experience with Terrorism," another explanation for a drop-off in spending is the change in the perceived risk faced by Americans.

"There is no question that spending on security and counter-terrorism increased after 9/11 and now, 10 years after the attacks, things are changing on the perception of the spending," Simon told AFP.

"When you combine the 10th anniversary with the killing of bin Laden, there are a number of people who are viewing the future as less spending. Because in terms of the perception of the threat, it may have diminished," he said.

"Any security company has to be flexible and adaptable."

Southers said companies should focus investment on new technologies.

"We're dealing with a very intelligent and adaptable adversary," he said. "Our technology has to be dynamic as well.

"Even though we had good technology 10 years ago, now it's about technology being better, more intuitive and be able to detect things that we didn't have as a threat 10 years ago."