Terrorists and Hackers

An "old" video story about "terrorist"/hacker Gary McKinnon.
It is unbelivable how easy you can pass some military security systems. I my opinion the true "terrorist" is the IT administrator or the person who hire the "Admin" on this job.

1. First of all how is possible to access the INTERNAL network of a military institution directly?
2. How is possible to don't have any firewall ?
3. How is possible to have blank passwords ?