(MONEY Magazine) – When it comes to policing online stock bulletin boards, the SEC talks pretty tough. Its enforcement Website lists cases brought against stock pumpers big and small. An agency spokesman says that it monitors boards regularly and that the size of a scam doesn't affect the decision to bring a case.

But as Columbia University law professor John Coffee notes, proving that someone talking up a stock is deliberately misleading investors, as opposed to going overboard in his enthusiasm about something he owns, isn't easy. Moreover, says Coffee, the thousands of boards now on the Web are more than the SEC can effectively monitor. And, he notes, a trader with larceny in his heart can take electronic steps that make it very hard to determine his identity.

--Brian Murphy