I can't imagine it is. I have had auth.net running for over 3 years and suddenly it changes. It's not too hard to install a couple new php files into the directories and configure authorize.net. The overall problem, I believe is with cURL. I may just change to SIM to at least keep my merchant account going, since PayPal is so expensive.
It's obvious there are huge problems with the authorize.net AIM module. Now I know this is an open source free product, but some of us paid lots of money for a template that now doesn't process transactions that it did only a few months ago. I've been in financial services tech support for years and if many people are getting the same error running the same code with the same set up on the authorize.net gateway, there's a problem with the module. Someone has to fix this. You cannot run an e-commerce shop without an e-commerce payment processing application.