Snapping the three-day rally, the Bombay Stock Exchange benchmark Sensex today fell by over 268 points as investors booked profit after the scaled a 17-month high last week amid weak global trends.The 30-share Sensex, which had gained 441 points in the last three sessions, lost 268.14 points to 16,866.41 points.The wide-based National Stock Exchange index Nifty also fell by 80 points at 5,003.