A weird bug on Facebook is congratulating people on 46 years of friendship — even though most of them are younger than 46 and the site has been around for less than a quarter of that time.

As spotted by Vox's Lauren Katz, who is 24:

This is probably the result of something called "epoch time," which is a way the Unix operating system records time. Epoch time is the number of seconds that have elapsed since midnight on January 1, 1970.

Many servers use Unix, so a lot of programming is based off epoch time — and January 1, 1970, was 46 years ago.

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