United Airlines and Wall Street Journal also went down today. The Chinese market is also in chaos today. Markets around the world are down due to the ongoing economic crisis in Greece after they voted no to Europe's bail-out offer. And (last week) US stocks also had the worst week thus far this year.
And yet, incredibly, all of these seem to be unrelated.
That certainly seems to be the official line, although it doesn't seem impossible that it could be an attack either; plenty of high profile attacks have occurred recently. China is under pressure, and events in Greece weakening American and European markets would make this an opportune time to strike. It would take more investigative journalism to provide evidence of what really happened, though. I don't trust the NYT to deliver much more than PR releases of the affected corporations and governments. I've seen some people linking this norsecorp.com map when speculating, which seems like something made in part or whole by the USG.