The New York Times put an article out on Sunday looking at increased Russian naval interest in the world's submarine cables. The worry is that anyone with a submarine fleet could take down the world communications net for extended periods quite easily with a few simultaneous cuts in deep water. How seriously should we take the idea?
Oh, it's definitely a threat. But I suspect that it's mainly a defensive threat, meant to discourage any ganging up on Mother Russia by the West over something within or adjacent to its borders like Ukraine. Russia doesn't have the ability to project force globally on a sustained basis other than via nuclear means. Threatening to cut the cables gives them a way to retaliate without escalating all the way.
But using it offensively would be the single greatest way to unify Russia's enemies. Far too many economies depend on the bits that flow through these cables for such a situation not to escalate, and they have to know that.
That's not to say that there is no cause for concern of course. Yet there's not all that much that anyone can do about Russia's newfound interest in such things. 6000+ miles of submarine cable lying on the ocean floor is not something one can hope to fortify. It's a soft target, and it's no mistake that we are being reminded of that.