By all appearances, Raj Rajaratnam was a self-made billionaire, having built Galleon Group into a giant hedge fund with a specialty in technology companies.

But prosecutors said on Friday that he had profited not from his trading genius but from his Rolodex, and they arrested him on charges of conspiracy and securities fraud in what they called the biggest insider trading scheme ever involving a hedge fund.

In all, six people were arrested, accused by prosecutors and the Securities and Exchange Commission of earning more than $20 million from illegal trading in companies like Google, Akamai and Hilton Hotels over nearly three years.

Even now, after the discovery of Bernard L. Madoff, the scheme outlined by law enforcement officials is the stuff of Wall Street thrillers, not seen since the days of Ivan Boesky two decades ago. Mr. Rajaratnam is accused of tapping a vast network of informants across a swath of corporate America: a senior official at I.B.M. considered a contender for the top job at that firm; executives of Intel and the consulting firm McKinsey & Company; two former Bear Stearns employees who had moved to a hedge fund, New Castle Partners; and an analyst at Moody’s Investors Service.