Hi, it does sounds like your installation has been compromised.
I would recommend as you have done:
- Change all admin passwords
- Change server access credentials
- Ensure you have all security patches installed
- Review all code to ensure that no hacked code remains
- Review admin area configuration such as the Miscellaneous scripts section to ensure nothing untoward has been placed in there.
- If you can, check that no additional database triggers have been added.
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