I saw a request in my apache error logs for:

Surprisingly, it was showing a 200 (successful) code.

If I go to domain.com/9a5291e45c80ddb8cfde7e51c7a2c7e85a2dada7.php I get a blank white page instead of a 404 page not found error message.

Any other combination of numbers and letters will result in a 404 error message, but that particular page seems to show a white page.

The same is true with other Wordpress websites:
https://premium.wpmudev.org/blog/9a5291e45c80ddb8cfde7e51c7a2c7e85a2dada7.php (white screen)
http://wpmudev.org/9a5291e45c80ddb8cfde7e51c7a2c7e85a2dada7.php (white screen)

Google returns no results for 9a5291e45c80ddb8cfde7e51c7a2c7e85a2dada7.php

Any ideas what this mysterious page is??