I fixed it.
This is what I got from the hosting service:
Hello,
Thank you for contacting us.
At around 4am EST, our system administration team identified a website defacement attack affecting a large number of customers. We are still investigating, but it appears that files named index.php have been defaced. We are evaluating how this has occurred and our security team will have more information shortly. Our systems team is working on an automated fix, but in the interim, if you have a backup, you may upload your index.php files
to correct this. You may need to do this for each directory. If your site uses an index.html or index.htm, you will need to upload those files, then delete the index.php. Please see the link below.
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Anyhow, I loaded backups for the site and all is well again.