If you’re running Windows 7, and you haven’t already installed Service Pack 1, you should do so before April 9, 2013. After that date, Microsoft will no longer provide patches for Windows 7 without SP1. That includes security patches.

Microsoft will continue to supply patches for Windows 7 with SP1 until January 14, 2020.

The details are laid out in a related post on Microsoft’s Springboard blog.