The venn diagram of people who can afford autonomous wire-cutting submarines and people who can hire accountants to hide white collar insider trading fraud is a circle.

Most "evil plans" are subverted by the fact that it's literally easier to just become rich and powerful in traditional/corrupt ways than to try to execute some elaborate scheme with espionage and robotic inventions.

There are plenty of approaches that have been developed over the centuries for dealing with nefarious actors (usually pirates) on the high seas.

The tools employed can be blunt and destructive.

Cables are cut all the time just by eg anchors; I don't think you'd need a sub. The hard part would be finding the cables though, since their position isn't publicized to prevent this sort of thing. Plus the place where it'd be easy to do this, on the continental shelf, is probably in territorial waters.

You're kidding right? There are giant maps of these cables all over the place.

Maps that show exact location? Ocean’s big.