These kinds of attacks, which are loud, aggressive, and have limited real-world effects, are basically a form of psychological terrorism. It's much more about fear and pressure than it is casualties.
NEW: Here's what we know, and don't know, about the cyberattacks that have hit water plants across at least 12 states in the U.S. in the last couple of weeks. The wave of attacks, allegedly carried out by Iran's government, are more widespread than previous attacks on critical infrastructure.