From the IRS:
An identity protection PIN (IP PIN) is a six-digit number that prevents someone else from filing a tax return using your Social Security number (SSN) or individual taxpayer identification number (ITIN). The IP PIN is known only to you and the IRS. It helps verify your identity when you file your electronic or paper tax return. Even though you may not have a filing requirement, an IP PIN still protects your account.
If you would like to enroll, renew or change your health insurance plan with the Marketplace for 2016, please be aware that the open enrollment period is now active and runs from November 1, 2015 through January 31, 2016.
Visit HealthCare.gov for more details.