Byline: Mark Schwanhausser

Oct. 10--The Securities and Exchange Commission could put a chill this week on automatic stock-trading plans that scores of Silicon Valley executives use to insulate themselves from allegations of insider trading.

SEC enforcement chief Linda Thomsen warned seven months ago that the agency was taking a "hard" look at such plans, citing a Stanford University researcher's study that found executives who used them had generated much better returns than those who didn't.

Thomsen is scheduled today to delve into these so-called 10b5-1 plans -- named after a section of securities rules -- at a conference in San Francisco. Although the SEC ...