Homeland Security gives receiver manufacturers best practices for dealing with the recent leap second event
(UPDATED January 1, 2017) A positive leap second was inserted between second 23:59:59 UTC of 31 December and second 00:00:00 UTC of 1 January 2017. This extra second is displayed on UTC clocks as 23:59:60. The last leap second was introduced in UTC on 30 June 2015 at UTC 23:59:60
By Inside GNSS