Last week the authorize.net changes were put into effect. The notices went out a very long time ago but for some too long ago.

If you are using the SIM module (payments take place off your website), you have to upload the new file to the includes/modules/payment folder. Then you must generate a new signature key in your a.net account.

But really why are you using it? Just as easy to get the needed data for the AIM module that processes credit cards onsite. As long as you have a secure certificate, you are not endangering your website or your customers and in the end may well increase your sales.

If you are using the AIM module, just erase the MD5 hash if you are using it. If you aren’t, you don’t need to worry at all!

Instructions and full information : https://www.zen-cart.com/showthread.php?224911-Authorize-net-phasing-out-MD5-Hash-Key-option-Jan-2019

Contact me if you need assistance with either. I’ll be glad to help!