Later the team reported two flaws in their equipment set-up that had caused errors far outside their original confidence interval: a fiber optic cable attached improperly, which caused the apparently faster-than-light measurements, and a clock oscillator ticking too fast.
Comments
The article is from 2011, but it's somehow trending now and has been resubmitted a few times.
The origin of the mistake was found a few months later: https://en.wikipedia.org/wiki/Faster-than-light_neutrino_ano...
Obligatory xkcd: https://xkcd.com/955/