Doomsday Came About Every Five Years
Someone Out There really hated humans. Twenty years have passed since Shiva I first swept aside Earth's crude defenses and rained down destruction. Now Shiva V has entered the Solar System, more powerful than any of its predecessors.
The Shiva cannot be destroyed by fleets of ships: we tried, and it was the fleets that were destroyed. It cannot be defeated by a clandestinely developed super-weapon based on new principles of physics: no such weapon exists. It cannot be defeated by a forceful American President and his faithful generals: they do not know what to do.
There is only one way to defeat a Shiva: get inside and kill it. Once again, in the personae of five champions, four billion of us are about to do just that.
Written before the internet got up to speed. Marc Stiegler, the author, is an IT guy so what he speculated about the internet is not only possible but some of it has already happened.
It's only one of perhaps a hundred or so FREE BOOKS in the Baen Free Library. Baen is perhaps the best publisher for Science Fiction books. I own a BUNCH of them