In an essay written for the Lawfare blog, Schneier, an inventor of the Blowfish, Twofish and Yarrow algorithms, said that the probes which had been observed appeared to be very carefully targeted and seemed to be testing what exactly would be needed to compromise these corporations.
Schneier said he did not know who was carrying out the probes but, at a first guess, said it was either China or Russia.
Pointing out that the easiest way to take a network off the Internet was by using a distributed denial of service (DDoS) attack, he said that major firms that provide the basic infrastructure to make the Internet work had recently seen an escalation of such attacks.
It also looked like the attackers were probing to find out the exact point at which the network being probed would cave in. "One week, the attack would start at a particular level of attack and slowly ramp up before stopping. The next week, it would start at that higher point and continue. And so on, along those lines, as if the attacker were looking for the exact point of failure," Schneier wrote.
Security guru Bruce Schneier.
Another aspect of these attacks was that they seemed to be aimed at finding out the extent of a network's defences. There were more vectors involved, meaning that the targets had to counter with differing defences.
"This means that the companies have to use everything they've got to defend themselves. They can't hold anything back. They're forced to demonstrate their defence capabilities for the attacker," he wrote.
Schneier said he could not provide details as the information had been given to him on the promise of secrecy, but added that what he was hearing was consistent with what had been reported by Verizon in its second quarter report on DDoS trends: "in Q2 2016, attacks continued to become more frequent, persistent, and complex."
And finally, he said, one company had told him that it had experienced a number of probing attacks in addition to the DDoS attacks: the ability to change Internet routes and addresses was being tested and also the time between attack and response.
Schneier's conclusion? "Someone is extensively testing the core defensive capabilities of the companies that provide critical Internet services."
He said while there had been speculation as to the source, nobody really knew. Only the National Security Agency, which had more surveillance of the Internet backbone than all other players combined, would have a better idea. However, unless the US decided to create an international incident by naming names, there would be no attribution.
"But this is happening. And people should know," Schneier said.