(By Shah Gilani ) When it comes to the U.S. credit crisis, we've all heard the numbers. The stock market decline wiped out $7 trillion in shareholder wealth. It forced the federal government to commit to $11.6 trillion in bailout programs and stimulus spending. And it's led to the longest U.S. downturn since the Great Depression.

Everyone also knows that some of the key culprits behind this financial mess were the credit-rating firms like Standard & Poor's and Moody's Investors Service, which assigned top-tier "AAA" ratings to investments that were actually backed by subprime mortgages and other toxic debt.

Whether it was collusion or incompetence almost didn't matter: The firms claimed that the credit ratings they issued were constitutionally protected free speech. With this First Amendment shield, S&P, Moody's and others said they were protected from lawsuits or other liabilities.

But that's about to change.

A federal court judge in New York last week stripped the ratings firms of that defense, a decision that could expose the companies to billions of dollars worth of liabilities from investors who were burned by the faulty ratings.

Let's legal case involved three specific firms – two firms that rated collateralized debt securities, and an investment bank that sold the debt. Those three companies were:

• Standard & Poor's, which is owned by The McGraw-Hill Cos. Inc. (NYSE: MHP).
• The Moody's Investor's Service unit of Moody's Corp. (NYSE: MCO), which is 19% owned by Warren Buffett's Berkshire Hathaway Inc. (NYSE: BRK.A, BRK.B).
• And Morgan Stanley (NYSE: MS).

This particular case had been brought against Moody's and S&P by Abu Dhabi Commercial Bank PJSC and Washington State's King County. The case involved losses suffered from an investment in a structured investment vehicle (SIV) called Cheyne Finance.