Under certain conditions, systems with Skylake or Kaby Lake processors can crash due to a bug that occurs when hyperthreading is enabled. Intel has fixed the bug in a microcode update, but until and unless you install the update, the recommendation is that hyperthreading be disabled in the system firmware.
All Skylake and Kaby Lake processors appear to be affected, with one exception. While the brand-new Skylake-X chips still contain the flaw, their Kaby Lake X counterparts are listed by Intel as being fixed and unaffected.
Systems with the bad hardware will need the microcode fix. The fix appears to have been published back in May, but, as is common with such fixes, there was little to no fanfare around the release. The nature of the flaw and the fact that it has been addressed only came to light this weekend courtesy of a notification from the Debian Linux distribution. This lack of publicity is in spite of all the bug reports pointing to the issue—albeit weird, hard-to-pin-down bug reports, with code that doesn't crash every single time.