U.S. shoppers spent more online than in retail stores during the shortest winter shopping season in the past six years, with online sales hitting a record high, a report by Mastercard Inc (MA.N) showed.The holiday shopping season is a crucial period for retailers and can account for up to 40% of annual sales. But this year, Thanksgiving, which traditionally starts the U.S. holiday shopping period, was on Nov. 28, a week later than last year’s Nov. 22, leaving retailers with six fewer days to drive sales between Thanksgiving and Christmas. “Due to a later than usual Thanksgiving holiday, we saw retailers offering ... (full story)