Re: vulnerable? Who, us?
It would be really hard to interrupt the routing to all four. Each has a bunch of places where they can reroute traffic, so you can't attack a physical place to interrupt their service. Meanwhile, if you tried something like a BGP hijack, you'd have trouble getting all the networks to go through you and those which did would quickly realize their mistake when everything breaks. Also, if you did interrupt service, a lot of the world would be annoyed but many things wouldn't break. Take El Reg. There are Google and Facebook URLs in their pages, so they'd get blocked by this plugin. However, if Google and Facebook go down, their site still works. It's not hosted on AWS or Azure either, so you could cut all four and the only thing that would change is that there wouldn't be so many ads and the Facebook share button would go away. I've emulated that on my network on purpose anyway.
Biting the hand that feeds IT
