"In June 2017, International Business Machines
(IBM) initially discovered the firmware bug ...
and developed a fix, made publicly available in a
November 2017 microcode bundle. In
December 2017, the IRS agreed with the
contractor recommendation to remain on the
older microcode bundle for the 2018 Filing
Season because it was considered more stable... On Tax Day, April 17, 2018, the IRS experienced a storage outage due to a firmware bug on one
of the IRS’s high-availability storage arrays. Because of the outage, 59 tax processing systems,
including the Modernized e-File (MeF) system, were unavailable for approximately 11 hours
between 2:57 a.m. and 1:40 p.m.4"