Researchers from Ben-Gurion University of the Negev’s Cyber-Security Research Center say a malicious attacker can leverage a botnet of infected smartphone devices located throughout the country to knock the 911 service offline in an entire state, and possibly the whole United States, for days. The problem is in the fact that current US Federal Communications Commission (FCC) regulations demand all calls to 911 must immediately be routed to emergency services, regardless of the caller’s identity. Such attacks are currently difficult to block, as PSAPs have no way to blacklist fake calls.
Source: https://thehackernews.com/2016/09/hacking-911-emegency.html