Last night a vulnerability in Mac OS High Sierra was publicized. To summarize, it allows someone to gain admin access to your mac by using the root account and a blank (!) password. This flaw affects all versions of Mac OS High Sierra (OS 10.13.x).
It does not affect PCs, or Macs running older versions of the OS (anything 10.12 or below, Sierra, El Capitan, Yosemite, etc).
Apple just released an emergency patch for this flaw, so OIT is strongly recommending you run the fix right now.
Simply go to your Apple Menu and choose App Store, then Updates.
The fix is called Security Update 2017-001.
More information about this update is available from Apple: http://support.apple.com/kb/HT201222