There is a possibility to disable access to the front of your site.
How to enable the offline page?
Step 1: Go to "System → Global Configuration → Site".
Step 2: Click on "Yes" for "Site Offline" option.
Step 3: Fill in a text for "Offline Message" to give your visitors some explanation about why your website is unavailable.
Step 4: Click on "Save" to save your settings.
How to customize the offline page?
You need to edit the following file: /templates/jm-template/offline.php