Apache web server allows directory browsing by default,With directory browsing enable, will put your WordPress blog into danger and make it easy for hackers to look into your directory/files structure.
Many WordPress experts recommend to disable directory browsing for security aspects.To disable the directory browsing you need to edit .htaccess file.
Open your .htaccess file
Add this single line into your .htaccess file
Options -Indexes
The directory browsing feature should be disable now.