NEW YORK — The aggressive push federal prosecutors are making against potential insider trading is sending investigators into a legal gray area that may redefine insider trading itself.

Mutual fund company Janus Capital Group said Tuesday it was cooperating with an inquiry on insider trading. A day earlier, the FBI searched the offices of three hedge funds in New York, Connecticut and Massachusetts as part of what outside experts say could turn out to be one of the largest probes in Wall Street history.

Investigators are thought to be pursuing suspicions of trading by hedge funds and mutual funds that might have profited illegally using inside information not available to ordinary investors.

But the behavior being targeted by investigations appears more elusive and complex than the common understanding of insider trading – high-powered executives picking up the phone, whispering secret tips about big deals, and trading stock at an unfair advantage. These were the types of cases that ensnared executives such as Ivan Boesky in the 1980s and Enron’s Jeffrey Skilling more recently.

How the alleged scheme may have worked is unclear. Federal prosecutors declined to comment on Tuesday. But what is clear is that the way information is shuttled around the world of finance today is faster, more complex and more shadowy. It involves an increasingly digitized financial world where networks of insiders can share bits of information with blinding speed.

It can also tap into so-called expert networks of industry analysts, experts and consultants who squirrel details between corporate America and Wall Street about what companies are up to – potentially giving some investors an unfair edge.

Federal authorities have traditionally pursued high-ranking executives and their confidants in insider-trading cases. Now, they’re increasingly going after the rank and file. In September, for instance, the Securities and Exchange Commission accused a railroad supervisor and a trainman of insider trading after the workers noticed an “unusual number” of tours of people in “business attire” in a railyard.

The two men and their relatives then bet in the stock market that the company would soon be taken over and made $1 million when that turned out true, according to the SEC suit.

The federal crackdown on insider trading tis being led by Preet Bharara, the top federal prosecutor in Manhattan. Bharara has called insider trading “rampant.”

In a speech to the New York City Bar Association, Bharara said detection of insider trading has “perhaps never been more difficult to attack through traditional investigative means.”

The explosion of financial information, including blogs, tweets and online newsletters, makes it easier for an accused insider trader to argue that he or she was acting on information “based on some report somewhere,” he said.