Job Title: Corporate investigator Employers: Business intelligence outfits Openings:  Get training in law, accounting, journalism, or law enforcement first Salary Cap: High six figures Number of Jobs: Several thousand worldwide

A few months ago, Bob Brenner was asked to tail Steve Jobs. A certain hedge fund, which he won't name, wanted him to uncover the truth about Jobs' health after the Apple C.E.O. appeared frail and gaunt at Apple's July iPhone launch. Depending on the feedback, the hedge fund would shift its positions in Apple accordingly.

Brenner, who works for Kroll, the $1 billion corporate intelligence consulting firm, said thanks but no thanks, citing ethical concerns.

As head of Kroll's business intelligence group in the U.S. and Canada, Brenner is an expert at digging up hard-to-find information, and working for hedge funds constitutes a growing part of his business. But even corporate sleuths—please don't call him a spy—draw the line somewhere. "You could debate the question whether Apple has an obligation to their shareholders to disclose more than they have given the central position Jobs holds relative to the company's success," Brenner says. "We get hard-to-find information, and sometimes it's information subjects would prefer wouldn't be out there. But there's a personal sphere of privacy we won't get involved in. We're not going to do it."

There's a lot, however, that Brenner will do. The former New York prosecutor and one-time special assistant U.S. attorney leads a Mission: Impossible-style team of former lawyers, C.P.A.'s, financial journalists, police officers, and government intelligence experts. While they don't tail people to doctor's appointments or do the sort of illegal pretexting that got Hewlett-Packard into trouble several years ago, they will track down obscure sources, verify companies' claims with field research, and exhaustively search public records to gather information that a client could use to decide whether to invest in a company—or potentially even bust it for fraud.

In one well-documented case, Greenlight Capital C.E.O. David Einhorn employed Kroll (although not Brenner specifically) to assess the financial stability of Allied Capital and to look into possible fraudulent activity at its subsidiaries. The controversial six-year battle resulted in S.E.C. sanctions, a Justice Department indictment, and actions by the Small Business Administration that put Allied out of the government-based loan business.

Kroll doesn't usually work with short sellers like Greenlight, but with traditional long/short funds or funds that are looking to do straightforward investments in public or private companies. As a result, Brenner says he's doing an increasing amount of due diligence work, such as reviewing a C.E.O.'s track record or uncovering problematic issues a company might have.

In such cases, hedge funds prefer working with corporate investigators instead of other types of research outfits because they're discreet: Whatever information Kroll turns up for a client stays with the client, Brenner says. "If we get hired, we aren't writing reports for all the hedge funds. That gives them a competitive edge."

While the 48-year-old Brenner says he'll always treasure the time he spent in the courtroom, corporate work is more lucrative and just as challenging. "I could be investigating the death of a journalist in Ukraine one day and the next day be tracking sources of counterfeit goods in China," he says. "It's stressful but rewarding for anyone who enjoys the chase, solving problems, and finding the needle in the haystack."