Bruce Schneier points out in this post that over the past year or two, someone has been probing the defenses of the companies that run critical pieces of the Internet. He likens it to the US's Cold War program of flying high-altitude planes over the Soviet Union to force their air-defense systems to turn on, to map their capabilities.
Who would do this? It doesn't seem like something an activist, criminal, or researcher would do. Profiling core infrastructure is common practice in espionage and intelligence gathering. It's not normal for companies to do that. Furthermore, the size and scale of these probes -- and especially their persistence -- points to state actors. It feels like a nation's military cybercommand trying to calibrate its weaponry in the case of cyberwar. What can we do about this? Nothing, really. We don't know where the attacks come from. The data I see suggests China, an assessment shared by the people I spoke with. On the other hand, it's possible to disguise the country of origin for these sorts of attacks.