The Basics:
What: A password cracking contest sponsored by KoreLogic.

Where: DEFCON 23 at Paris & Bally's in Las Vegas.

When: The main contest lasts 48 hours:
11:59:59 PM PDT Thursday Aug 6 - 11:59:59 PM PDT Saturday Aug 8, 2015

Who: Teams with at least one team member attending the conference.

Why: To help push the envelope of password cracking techniques / methodologies and win a prize while you are at it.

Winning: There were prize pools for a "Pro" class and a "Street" class of competitor.

Updates: Watch @CrackMeIfYouCan for updates.