Leap second is a one-second time adjustment that is added to Coordinated Universal Time (UTC) in order to keep its time of day in synch with the mean solar time, or UT1. The one-second adjustment is applied to accommodate the minor slowing in the Earth's rotation. Since the leap second was introduced in 1972, 26 such leap seconds have been inserted. The most recent one happened on June 30, 2012 at 23:59:60 UTC. The next leap second will be inserted on June 30, 2015 at 23:59:60 UTC (19:59:60 EST).
As far as we know the MF Security portfolio is ok, the past 26 adjustments have not been an issue. We checked back on issues from the last adjustment, 6/30/2012, and there has been no fallout.