Massachusetts fined Morgan Stanley & Co. LLC $5 million over allegations it disclosed financial details about Facebook Inc. with institutional bankers that it hid from the public ahead of the social media network’s disappointing debut on Wall Street in May.

Secretary of State William Galvin charged that a senior investment banker at Morgan Stanley, the lead underwriter for Facebook’s $16 billion public offering, conspired to keep lower revenue projections for the company out of US Securities and Exchange Commission filings that are available to the general public.