Yesterday I wrote about how Goldman Sachs and DST is investing in Facebook at a $50 billion valuation. The two companies are investing $500 million. It turns out that Goldman Sachs is setting up a “special purpose vehicle” to allow their wealthy clients to invest in Facebook, which is still a private company. However there is an SEC rule that may consider this move illegal.

Even though companies like Facebook, LinkedIn, Twitter, and Zynga are private, you can still buy stock in them. The U.S. Securities and Exchange Commission (SEC) is now investigating the background of this private stock trading and is conducting investigations. The SEC sent out requests for information from the companies that facilitate the private company stock trading.

The SEC is investigating the departure of former Hewlett-Packard Company (NYSE:HPQ) CEO Mark Hurd. Hurd is believed to have shared inside information with a former H-P event hostess in 2008 about the company’s $13.9 billion acquisition of EDS.

Mark Cuban is one of the craziest billionaires in the world. He is offering to finance an investigation against himself… The SEC is investigating Cuban for an insider trading case and they told him that their lawyers could take up to 8 months to look into the full investigation. Cuban wants the case to speed up so he is offering to fund part of it himself. The SEC told Mark that they hope to get their lawyers started on the case by next March so that the documents are ready to go by 2012. Cuban would pay the overtime fees for the lawyers or retaining lawyers on a freelance basis. [New York Post]