Phoenix, Arizona - Police are investigating an act of vandalism that left many in northern Arizona without voice communications and Internet access last Wednesday when a fiber optic cable was cut north of Phoenix. This outage effected everyone in the area including emergency services and businesses who were unable to process any credit or debit card transactions.
http://www.usatoday.com/story/news/nation/2015/02/26/poliice-probe-arizona-outage/24043367/
This is just another example of how networks are vulnerable at the physical layer and investment in network infrastructure security must be considered.