When using the system for payment processing, often third party entities will contact you about Payment processing and PCI compliance. Most of these third parties are SPAM and should be ignored as your site does not require PCI compliance. The reasoning is that PCI compliance is maintained at the actual payment processor where the card is charged and data is potentially stored.
When customers use your site and checkout through the Authorize.net payment processor, the customer does appear to enter data on your site, but the data is passed securely via https to Authorize.net for processing and therefore Authorize.net is where the PCI compliance is maintained. Our system does not store any financial data, only customer address and order information.
Therefore, you do not have to worry about PCI compliance with your website on our system. If you feel doubtful, you can always contact your Authorize.net support contact or merchant account provider directly to confirm (use the info you received when you setup your account) and they can confirm this information and more than likely ensure you that the notifications did not come from them and that you are okay.