Just before the stroke of midnight Tuesday Coordinated Universal Time (UTC), computerized clocks around the world will pause for a moment to squeeze in an extra second.

The leap second, as it’s called, is needed to keep UTC in line with solar time. The two get out of whack due to changes in the earth’s rotation, and 25 leap seconds have been added to clocks since 1971. Network Time Protocol (NTP) helps regulate the official time among Internet servers, keeping it in sync with UTC.

But the last leap second in 2012 took some IT companies and other firms by surprise, and caused websites including LinkedIn and Reddit, as well as Qantas’ passenger reservation system, to crash. The problems involved unpatched Linux OS kernels, Hadoop instances, Cassandra and MySQL databases and Java-based programs.

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