Firewall

The Firewall is one of the most important softwares, since it's blocks invaders from entering in your VPC. It can be obtained by hacking some websites or by simply stealing it from other players.

Hacking
When hacking a VPC/website with a firewall, you must have a waterwall of a higher level in order to crack the password.

Protection
Having a firewall will stop hackers from invading your system, in case their waterwall is below your firewall's level. If it's the same or higher, you must get a better one to stop them from entering your system.

Note, however, that as long as the hacker has your computer's password, he can enter no matter how good the firewall is.