The hacker doesn't even need to be in the same ZIP code to crack a firewall or VPN -- the 3G link lets the Power Pwn take bash command-line instructions through SMS messages and doles out some of its feedback the same way.
While it sure ain't pretty, the Z100G should keep you relatively safe behind its variety of security measures, including firewall, antivirus, and intrusion prevention, in addition to remote access VPN and secure remote desktop features.