I'm in the SF Bay Area and after looking at traceroutes and packet loss it looks like something at PAIX has failed between Comcast, Hurricane Electric, NTT, and others.

A coordinated attack could be a cause of something like this, but more often than not it's a hardware or power failure at a critical exchange like PAO, DFW, IAD, etc. Also possible, human error in turning down traffic to certain servers, networks, and IP ranges.