Keep Practice to change the default credentials immediately to prevent such situations with readymade apps:

Here are some samples

>> WordPress:

Admin Backend URL: http://yourdomain.com/wp-login.php
Administrator Login ID: admin
Administrator Password: adminadmin

>> Joomla:

Admin Backend URL: http://yourdomain.com/administrator
Administrator Login ID: admin
Administrator Password: adminadmin

>> Prestashop:

Admin Backend URL: http://yourdomain.com/admin888
Administrator Login ID: [email protected]
Administrator Password: adminadmin

>> Opencart:

Admin Backend URL: http://yourdomain.com/admin
Administrator Login ID: admin
Administrator Password: adminadmin

>> Orchard:

Admin Backend URL: http://yourdomain.com/Users/Account/LogOn
Administrator Login ID: admin
Administrator Password: adminadmin

>> Moodle:

Admin Backend URL: http://yourdomain.com/login/index.php
Administrator Login ID: admin
Administrator Password: Admin@Admin123