On Sunday, YouTube became unreachable from most, if not all, of the Internet. No "sorry we're down" or cutesy kitten-with-screwdriver page, nothing. What happened was that packets sent to YouTube were flowing to Pakistan. Which was curious, because the Pakistan government had just instituted a ban on the popular video sharing site. What apparently happened is that Pakistan Telecom routed the address block that YouTube's servers are in to a "black hole" as a simple measure to filter access to the service. However, this routing information escaped from Pakistan Telecom to its ISP PCCW in Hong Kong, which propagated the route to the rest of the world. So any packets for YouTube would end up in Pakistan Telecom's black hole instead.It turns out the whole thing is due to a known vulnerability in the way routing tables work (full details are in the Ars article). But it's just crazy to see how fragile the internet is.
On the North American Network Operators Group (NANOG) mailing list, where many engineers in charge of Internet routing hang out, the consensus is that this was an accident. Only one or two people suggest that it may be a malicious act, possibly a trial of something bigger.