The 2012 Leap Second Bug refers to computer glitches and outages resulting from the leap second that added an extra second to June 30th, 2012 in order to keep atomic clocks in line with the planet Earth. An extra second is periodically added to the Coordinated Universal Time (UTC) in order to compensate for Earth’s inconstant speed of rotation.
A leap second was added to the Coordinated Universal Time at the end of the day on June 30th, and it contributed to numerous outages that were caused by leap second bugs in the kernel of Linux-based operating systems and also in some Java apps. Companies with servers impacted by the Leap Second Bug included Mozilla, Reddit, LinkedIn, StumbleUpon, Gawker, FourSquare, Yelp and several airlines running the Amadeus Altea airline reservation system.
Other companies such as Google have attempted to prevent any leap second bugs from impacting their servers by gradually adding milliseconds to their systems’ clocks prior to the officially recognized addition of a leap second.