The Earth's spin is gradually slowing down, by about two thousandths of a second per day, but atomic clocks are constant. That means that occasionally years have to be lengthened slightly, to allow the slowing Earth to catch up with the constant clock. At 11:59 p.m. on June 30, clocks will count all the way to 60 seconds.

However, the fear is that the move could wreak havoc on the infrastructure powering the Internet. This is not fud type story either. In 2012, much of the Internet crashed. Reddit, Foursquare, Yelp and LinkedIn all reported problems, and so did the Linux operating system and programs using Java.

The reset has happened 25 times since they were introduced in 1972, but the computer problems are getting more serious as increasing numbers of computers synchronize with atomic clocks. Apparently, these computers and servers are shown the same second twice in a row and they get very very stressed about it.

This particularly true if they are told to do an operation at the time that is repeated. An e-mail received in that moment, it could find its way in the wrong bit of the server.

Google built a smart update, which it called "leap smear" and modified its servers so that they would add a little bit of extra time every time they were updated, so that by the time of the leap second they were already caught up with the new time. It said when it laid out the plan in 2011 that it would use the same technique in the future, when new leap seconds are announced.