Twenty years ago this week, junk-bond king Michael Milken was sentenced to 10 years in prison after pleading guilty to six violations of securities law - none of which included insider trading. Still, the Milken case represented the high-water mark of a number of insider trading cases in the late 1980s,many of them linked or associated with the big buyouts of the era.

Insider trading didn't end with the Milken case. One of Minnesota's best known private investors, George Kline, pleaded guilty in 2001 to six counts of securities fraud, including using confidential information he gained as a director to profit on stock trades. The Kline investigation eventually ensnared eight individuals, including Kline and two of his sons.

But white collar criminal investigations seemed to back seat to terrorism and national security cases after 9/11, even during the buyout boom of the latter half of this decade. Insider trading didn't go away, but the government's attention certainly wandered.

Media reports over the weekend, and yesterday's raid of hedge fund offices suggest a new, more aggressive response to insider trading, which has become increasingly more complex. In a speech two months ago, the U.S. Attorney leading these cases, Preet Bharara, said insider trading is "rampant and may be on the rise," and that the people doing it are "are already among the most advantaged, privileged, and wealthy insiders in modern finance."

Bharara also noted that the volume and speed of stock trading today, coupled with the explosion of websites, blogs, newsletters and consultants, makes it harder than ever to investigate and prosecute insider trading.