The basis of trust for secure website connections—between you and a financial institution, you and Twitter, you and your health-care provider—relies on cryptographic shorthand. An outdated form of this shorthand will finally be mostly ditched starting January 1, 2016, and you may see the impact.
If you run websites, you’ll need to update the digital certificates that are used to form a secure session. But even if you’re just a surfer, you may still encounter problems with sites you frequently visit. Some sites, like Facebook, are trying to provide a smoother migration, though it’s very late in the figurative day to do so.