Before exposing a SharePoint farm to the internet it is important that precautions are taken to ensure that security cannot be compromised. Taking all reasonable steps to secure the environment should minimise the risk of a security breach. I have found the following 3 technet articles useful during this process, but they are not easily located when searching for them this morning.

 Web server: http://msdn.microsoft.com/en-us/library/aa302432.aspx

Application server: http://msdn.microsoft.com/en-us/library/aa302433.aspx

Database server: http://msdn.microsoft.com/en-us/library/aa302434.aspx#c18618429_015