Drupal Security: Forewarned is Forearmed
Yesterday, at 7.13pm, the Drupal Security Team issued a public service announcement: Drupal 7 and 8 core highly critical release on March 28th, 2018 PSA-2018-001.
This needs a bit of background to understand.
How Drupal Core Updates Normally Work
Updates to Drupal Core fall into one of new kinds.