WordPress file added deleteme.wp#######.php

I have been getting these warnings on a number of the WP sites that I manage where the Security plugin is installed. When I go to the log file and then click on the details, I see the logged item. It does not tell be exactly where the file was added. I then went to FTP and looked carefully and could not find the file. Exactly what is this? Exactly where do I find the place where the file was added?

https://ww.wp.xz.cn/plugins/better-wp-security/