It was the most hotly anticipated stock debut in years, raising $16bn, and valuing the social networking sensation, Facebook at $104bn. But now - just days after the fanfare - it's in another media storm. This time there are big rumblings around whether only a select few investors got preferential information about the firm's revised financial forecast before the stock hit the market last Friday.

Facebook's shares have dropped another 9% from its $38 per share start, amid concerns about the way that advisers from Morgan Stanley bank – the lead underwriter on the floatation - disclosed information to investors. The top securities regulator for Massachusetts, William Galvin, said he had subpoenaed Morgan Stanley, saying his office is investigating news that one of the bank's analysts had divulged the fact he'd cut his revenue estimates for Facebook to some clients and not others.

Other regulators have also said they're going to review the disclosure process. Meanwhile Morgan Stanley said what it did was "in compliance with all applicable regulations" and that it"followed the same procedures for the Facebook offering that it follows for all initial public offerings".

Facebook hasn't commented as yet, but there's no doubt this news has taken some of the shine off one of the stock market's most historic events.