The U.S. Securities and Exchange Commission (SEC) is examiningthe exposure of stock exchanges, brokerages, and other Wall Streetfirms to cyber attacks that have been called a threat to financialstability.

The SEC is holding a roundtable discussion of those risks inWashington today as it weighs a new rule proposal asking whetherstock exchanges should be required to tell members about breachesof critical systems. More than half of exchanges surveyed globallyin 2012 said they experienced a cyber attack, while 67 percent ofU.S. exchanges said a hacker tried to penetrate their systems.

The agency also will probe how companies are disclosing cyber threats to investors in publicfilings. Businesses including Target Corp., from which hackersstole payment-card data for millions of shoppers in December, arerequired to disclose such threats when the information would affectan investor's willingness to own the company's shares.