Web site defacement mirror Zone-H posted a revealing report on the recent defacement of their own site. The intrusion resulted from a combination of human and technical failures.
The moral of the story is that anyone can be compromised, because the attacker has the initiative. The attacker is usually more motivated and has more time, and resources than the defender. In a world where anyone can be compromised, there is no excuse for not monitoring and preparing for incident response. Every digital resource is a future victim.
The "solution" to intrusions is analog: arresting the intruders. It is not technical.