Foreclosure activity hit its lowest level in four years in 2011, decreasing by a third from the previous year according to data released today by RealtyTrac. One in every 69 housing units in the U.S. was subject to a filing during the year, 1.45 percent of the total housing stock. Activity also decreased for the month of December and for the fourth quarter of 2011 according to the U.S. Foreclosure Market Report covering the three periods which was released by the Irvine, California company this morning…