(FORTUNE Magazine) – The early August homeland security warning that Citigroup, Prudential, the New York Stock Exchange, and other large financial institutions on the East Coast could all be al Qaeda targets was chilling. But George Friedman had a different message for his FORTUNE 500 clients: Chill out. It didn't fit al Qaeda's usual plan of attack. Friedman's company, Stratfor Inc., is one of the elite but low-profile private intelligence agencies that are increasingly relied upon by multinational corporations, private investors, hedge funds, and even the government's own spy agencies for analysis of geopolitical risks.

Corporate intelligence-gathering has grown in both magnitude and sophistication since 9/11, experts in the field say, in part because big companies are either hiring or contracting with intelligence veterans. Lehman Brothers, for example, brought in Ted Price, former deputy director of operations at the Central Intelligence Agency, to be its head of global corporate security after 9/11. Senior security executives at big corporations meet regularly with local and national intelligence and law-enforcement agencies. But whenever there is an elevated threat--the current one started six months ago with rising insurgency in Iraq, the destabilization of Saudi Arabia, and the likelihood of an attack prior to the U.S. elections--many firms also turn to private intelligence analysts like Austin-based Stratfor, Jane's Information Group (an offshoot of the venerable British military catalogers), the Economist Intelligence Unit, and Marsh & McLennan's Marsh Kroll subsidiary.

Overall spending on corporate security and intelligence could reach $50 billion this year, says Brian Ruttenbur, homeland security analyst at investment firm Morgan Keegan. (That includes physical security, Internet safeguards, staff screening and training, and competitive intelligence, not just terrorist and related intelligence analysis.)

Many of these private intelligence analysts were trained by the CIA, the FBI, or the military or in spy organizations in Russia, Israel, and other foreign lands. One of Stratfor's top analysts, for example, is a former Soviet army colonel who, as a military intelligence officer in Afghanistan, got to study Osama bin Laden's tactics firsthand.

But the analysts are equally likely to be bright young scholars or tweedy librarians who sift vast amounts of public data, mixed with reports from human operatives around the globe, to find information crucial to a decision, say, to build a new plant in a country whose name ends with "stan" or to evacuate employees from the Middle East.

Jane's Information Group helps clients assess geopolitical risks from terrorism to organized crime, as well as security for buildings, pipelines, and "offices and subsidiaries in places that are sensitive or difficult," says Alfred Rolington, the group's CEO.

"Normally speaking, large corporations have planning groups staffed by sophisticated people, just as in government agencies with intelligence operations," Rolington says. "We're not trying to replace them. We give a second, independent opinion for our government and corporate clients, adding to their knowledge on anything to do with security protection and analysis."

Although he declines to name any of his clients--no private intelligence company with which we spoke would confirm links to any of the companies affected by this month's threat elevation--Jules Kroll, the founder of Kroll Inc., says his company has a long history of working with the types of financial institutions cited in the recent alert. Companies spent heavily to develop their own security and threat-assessment services after 9/11, he says, but now many often turn to outsiders for advice when there's a heightened risk.

Jane's offers off-the-shelf reports on current threats for as little as a few hundred dollars, but deeper access to its geopolitical and global terrorism databases can cost up to $100,000 a year. At Stratfor, daily newsletters and special reports are available by subscription on the web for a few hundred dollars, but corporate customers typically opt for detailed, in-person briefings that cost $10,000 to $50,000. Some retain Stratfor for ongoing consulting for as much as $20,000 a month.

Stratfor's price-of-this-magazine analysis on the recent warnings? While the overall risk of a terror attack in New York is the highest it has been since 9/11, he says, al Qaeda has never "attacked into an alert," meaning that once the government has publicly identified a potential target--even if it is erroneous--the terrorist group retreats and reassesses plans. And then the intelligence game begins anew. --Peter Lewis