Powerful forces have been probing the internet's underlying infrastructure for weakness using sophisticated distributed denial-of-service (DDoS) attacks, according to security expert Bruce Schneier.
Schneier said in a blog post that companies providing the basic infrastructure that makes the internet work have reported an increase in DDoS attacks against them over the past two years.
The probes appear to be carefully calibrated in order to find out just what it would take to bring the companies down.
"These attacks are significantly larger than the ones they're used to seeing. They last longer. They're more sophisticated. And they look like probing," he said.
"One week, the attack would start at a particular level and slowly ramp up before stopping. The next week, it would start at that higher point and continue."
The attacks have been carried out using multiple vectors, adding to the impression that the organisations' entire defence mechanisms are being tested.
Schneier's findings, which come from information provided to him by key internet infrastructure providers, are consistent with a report by DNS service provider and registrar VeriSign which also noted DDoS attacks that are increasing in sophistication.
The scale and intricate nature of the attacks suggest that nation state hackers are involved, according to Schneier.
"It feels like a nation's military cyber command trying to calibrate its weaponry in the case of cyber war," he said.
"It reminds me of the US Cold War programme of flying high-altitude planes over the Soviet Union to force their air defence systems to turn on, to map their capabilities."
It is impossible to pinpoint where the attacks originate, but they are consistent with the capabilities of a country such as China, Russia or indeed the US.
Taking down the web would presumably be a high-risk strategy as it would have severe knock-on repercussions for the attacking nation.
Encrypted email provider ProtonMail was knocked offline in November 2015 by "an extremely powerful DDoS attack" which the Swiss company put down to a state actor concerned about the secure communications service it provides for journalists and activists.
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