MDU Resources was downgraded to hold from buy at TheStreet Ratings on Tuesday. TheStreet Ratings gives MDU Resources Group a C+ grade.
Charles Schwab, Edward Jones, E*Trade Financial, Fidelity Investments, Morgan Stanley, Scottrade and TD Ameritrade are being probed.
TD Ameritrade CEO Tim Hockey talks with TheStreet.
U.S. stock futures are slightly higher on Tuesday, following the collapse of healthcare overhaul in the U.S.