I'm not sure what the 'following formats' are, but simply putting a $ in front of the letter will lock the column reference, and putting a $ in front of the number will lock the row reference. Putting a $ in front of both will allow you to keep the cell reference the same. For example: A1 should be A$1$ in an equation to keep the reference as A1 for all 'filled down' equations.
Firewall, just like encryption prevents unauthorized entry into a computer. However, Firewall can be implemented in both hardware or software form; or even a combination of both.