Magento Checkout Malware Cleanup & Upgrade

It has been one week since we switched back to Authorize.net hosted pop up form, and we have not had any issues until today where customers say it did not load, i checked myself and on first try incognito mode i got payment form with blank source. i checked and i suspect this has been added as card skimmer recently.

I would like a certified Magento developer to trace and remove every fragment of that code, then upgrade the site to the latest stable Magento release so this doesn’t recur.

During the process please:
• Audit the entire codebase (core, theme, custom modules) to identify injected scripts or compromised files.
• Repair or replace any affected files and confirm the storefront, admin, and APIs operate normally.
• Upgrade Magento to the newest official version, applying all security patches.
• Re-test the checkout until no errors or crashes appear and every payment attempt completes successfully.
• Confirm that no further unauthorized redirects occur—both automated scans and manual browsing should come back clean.

I run on a typical LAMP stack and use common payment and shipping modules, all of which need to stay operational after the upgrade. If additional patches or extension updates are required to maintain compatibility, let me know in advance so we can schedule them.

I’m looking for someone who has handled similar clean-ups, can start quickly, and is comfortable documenting exactly what was removed or updated for my records.