Is Moscow interested in cutting or tapping the cables? Does it want the West to worry it might? Is there a more innocent explanation? Unsurprisingly, Russia isn't saying.

But whatever Moscow's intentions, U.S. and Western officials are increasingly troubled by their rival's interest in the 400 fiber-optic cables that carry most of world's calls, emails and texts, as well as $10 trillion worth of daily financial transactions.

"We've seen activity in the Russian navy, and particularly undersea in their submarine activity, that we haven't seen since the '80s," Gen. Curtis Scaparrotti, commander of the U.S. European Command, told Congress this month.