This is a book that is as close to being a provisional five-star book as it is a two-star rating. It all boils down to how computer 'in the know' you are. Zero Day is a thriller for nerds and geeks and professionals in the business. And if you count yourself amongst them, then it's worth five stars. If not, well, your results may vary.
I'm not familiar with Howard Schmidt at all. His co-writer Mark Russinovich? Oh yeah. He's in the pantheon of best programmers on the planet right now. Currently he works for Microsoft, but such is his legend, that many MS-haters still love him and his work on a bunch of utilities everybody wishes were built into Windows. He's also the guy that caught Sony with their hands in the cookie jar when he exposed their rootkit shenanigans back in the early part of this century. Again, if you don't, or couldn't, follow what I just said, this book is going to be a bit difficult for you.
Having given you all the warnings I can, now let me continue with the plot.
Jeff Aiken and Daryl Haugen get tasked with stopping a nefarious plot to bring down the cyber infrastructure of the world (not just the States). A series of worms and virii have been let loose that seem to hide under the radar of the security community, even the government's not all in on how all encompassing the threat is. Aiken from the public sector and Haugen from the government side, do realize just how in deep the threat is.
Which leads the bad guys, and we ARE talking about organized bad guys of a particular political bent, to resort to hitmen to eliminate the duo. This is the thriller part the average non-involved computer pro can get with. In fact, the ending is pure Hollywood, Aiken and Haugen confronting the evil masterminds in their lair and emerging alive alone. The bad guys dying even as their schemes explode around them.
The whole book is, in my mind, a successful attempt to combine the cerebral world of computer hacking with the Bondian derring-do of modern day movies. I think Russinovich tries to make the jargon understandable, but I can't really be a judge to his efficacy.
Zero Day is a book that is supposed to entertain and terrify. Russinovich even writes that the bad guys were just unlucky not to have won the day. Cyber-terrorism is already a fact and it's only going to get worse if everybody, including the government, don't treat it more seriously.
You've been warned.