Locking Drupal from visitors?

Hello,

I am trying to discover if it is possible to lock a Drupal instance (Web site?) from public eyes. We are interesting in creating a Web page for our staff but do not want someone from the outside to accidently come across it.

For instance, if someone were to go to http://private.domain.com they would be able to see it now. Is there a way to lock it and put a password protected? Is it complicated?

Thank you.

Drupal version: 


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