NEW YORK, Oct 4 (Reuters) - U.S. stocks opened slightly lower on Monday after a ratings downgrade weighed on Microsoft and new Swiss banking rules raised fears of smaller bank profits.
* The Dow Jones industrial average dropped 12.79 points, or 0.12 percent, to 10,816.89. The Standard & Poor's 500 Index shed 2.25 points, or 0.20 percent, to 1,143.99. The Nasdaq Composite Index lost 7.94 points, or 0.33 percent, to 2,362.81.