You might want to notify your host immediately and ask them what changed on their configuration.
Also, how did you try to update the site?
The file can be created automatically if the web server runs as the same user as the files in WP directory, or has permissions to create a file. You might want to check that: for example, Apache web server, and PHP, runs as www-data in some default installations, but the files you upload will probably have your FTP user when you transfer them.
