Wall Street's industry-funded watchdog on Tuesday warned that scammers are turning to a rather old-fashioned strategy for defrauding investors—the phone call.

"In a new twist to Internet 'phishing schemes,' which use spam email to lure you into revealing everything from Social Security numbers to financial account information, it appears that some fraudsters may be resorting to a time-tested method—the telephone call," the Financial Industry Regulatory Authority (FINRA) said in a statement.