Mid Day Movers: VASCO Data Security International, Inc.(NASDAQ:VDSI), Omega Flex, Inc.(NASDAQ:OFLX), Landstar System, Inc.(NASDAQ:LSTR),By Stefan LevyApril 24, 2014 VASCO Data Security International, Inc.(NASDAQ:VDSI) is a strong gainer Thursday, trading to its best in 18 months, after its Q1 results…