Authorize.net TLS 1.2 D Day
Authorize.net will no longer allow TLS 1.0 or 1.1 as of is February 28, 2018.
This means the server your site runs on must be using TLS 1.2 by that date. To check you can use SSL Labs tool. If you don’t see TLS 1.2 enabled contact your hosting company immediately!
You can read more about TLS FAQs for additional information regarding TLS disablement.
It will also affect what browers you and your customers can use and you can find a list of acceptable ones here. Some older ones like Safari for Windows will stop working for https:// pages.
NOTE: PayPal and other merchant account gateways are also taking this route, given the need for PCI compliance. So if you get a notice from your gateway do not ignore!