Public Site Disappeared Due to Zero Byte Index File

The public portion of my site recently disappeared though the admin side still worked. Everything checked out until I viewed the file directory where I found two zero byte files, default.html and index.htm. Index.php couldn’t be found. I copied over an index.php from another WP site and that restored it.

I got this fixed, but I would just like to know if this was the result of a deliberate action by someone and whether I can prevent it in the future.