The SEC begins to probe into S&P for insider trading after it downgraded US credit rating on August 5.

The U.S. Securities and Exchange Commission will scrutinize the mathematical model used by Standard & Poor to downgrade the U.S. credit rating and whether any employees knew of the decision ahead of its announcement, the Wall Street Journal reported, citing people familiar with the matter.

The report said the SEC's review is part of a wider investigation of potential insider trading conducted by people who learned of the downgrade decision in advance.

The SEC set up a whistleblower Web site on Aug. 12 allowing tipsters to report any behaviors that violated regulations, Chinese financial news site Caing.com reported.

Previously, U.S. Treasury Secretary Timothy Geithner pointed out a US$2 trillion discrepancy in S&P's analysis of U.S. government finances. Geithner said the decision was a “terrible judgment” and its calculation method showed an amazing lack of common sense.

China's business press carried the story above on Monday.