A leap second was added to atomic clocks worldwide at 23:59:60 (or near midnight) at Coordinated Universal Time (UTC) on December 31, 2008. This is the 24th leap second to be added since the first leap second was added in 1972. This is also the first leap second in three years. The extra second is added to make up for the fact that the earth's spin is slowing down.
• How to catch a leap second