Andrew Ross Sorkin today tackles the issue of market rumors. He's with Jamie Dimon, and doesn't like them:

As Schulte Roth said in its note to clients, which include SAC Capital Management and Jana Partners, two big hedge funds, "spreading false rumors in order to induce others to trade in a company's securities constitutes market manipulation."
James Dimon, the chairman of JPMorgan, says rumor-mongering is unconscionable. "I think if someone knowingly starts a rumor or passes on a rumor, they should go to jail," he said on Charlie Rose's program on Monday night. "This is even worse than insider trading. This is deliberate and malicious destruction of value and people's lives."...
There's no way to quantify whether rumors are more rampant today than they used to be or whether they are just traveling faster. But what is clear is that there seems to be little being done about it. It might be difficult to make a case, but you'd think you'd see subpoenas flying at least as fast as the rumor mill.