Brian Krebs, a well know security expert, experienced a SWATing attack. For anyone not familiar with this term, the idea is simply that you call 911 and state that there is an emergency that requires a SWAT team to intervene. By calling 911 and spoofing your calling number, you can trick the SWAT team into showing up at your victims location/residence. It is trivial to spoof your calling number. It is also very easy to use free text to speech services to create an audio file that states the emergency, but avoids the attacker having to use their own voice.
This is an extremely dangerous attack. I fear this attack will become more common and it is a matter of time before an attack takes place and someone gets seriously injured.