System -> Configuration -> Design -> Footer -> Miscellaneous HTML
design/footer/absolute_footer Hackers embed malicious code.
Upgrading to Magento 22.214.171.124, or being hacked into malicious code to collect credit card data. Do not know how to fix this loophole, ask technical staff to help.
1. Please go to magereport.com and scan your site to find missing security patches.
2. Install the missing patches if any
Give Kudos if it helped or Accept it as a solution
@alphaAnThere are possibility your site may have hacked and it will require proper implementation of risk mitigation. Upgrading the site or implementing the security patch may not help as you are already affected. You can upgrade/install security patch to secure your site from future attacks.
Step #1 would be to scan your site code and database. You need to remove any malicious code you find in database or in the code.
Step #2 Follow the Magento Security Tips. You can follow the below URL as well to make your Magento more secure an avoid such issues in future.
Problem solved? Please give 'Kudos' and accept 'Answer as Solution'.
Many thanks to @hellotaran for solving these problems through your method. Thanks again.