Falling for the fourth straight session, the Sensex at the Bombay Stock Exchange tumbled 364 points, or 2 percent, to an over 4-month low of 17,507, on across the board selling, today. The Sensex had already lost almost 440 points in the previous three trading sessions. The Nifty at the National Stock Exchange declined 109 points, or 2 percent, to 5,258. Stock markets in China, Hong Kong and South Korea dropped between 0.4 percent and 0.8 percent, as Greece concerns lingered.