Update 1/4/2014 Replaced cache with something that should stand up to the salt water better.
Update 3/22/2004: Several of the logs give VERY generous hints, so if you want to experience the full 4.5 stars in difficulty, don't read the logs. 
Update 7/3/04 Added puzzle hint since there are now various versions of the same code book
Sgt Stitches ran breathlessly into the barracks. “Lt Happy Camper! Lt Happy Camper! Our patrols are reporting that all of our caches have been found and items that should be in them have gone missing and new items appearing in their place! So unless you believe in the “cache fairy”, that means someone out there is intercepting our communications and decoding our cache locations.”
“Yes Sergeant. I’ve seen the logs on net. We believe someone has been employing a classified super computer to guess our encryption keys. What we need is a code that is unbreakable by brute force.”
“Well, Lieutenant, I’ve been working on a new code ever since Cpl Coconut had his ear infection and I lost the coordinates for that cache.” Sgt Stitches reached into his backpack and threw down a small Brown and green book. “Here’s the new code book, Lieutenant. I’ve decided to call the code: Digital Fortress. Cool name huh?”
Lt Happy Camper skeptically examined the book, then looked up at Sgt Stitches. “This is the new code book? Are you sure this code will be unbreakable?”
“Only a human mind can break this code, and then, only if they have the code book. In fact, even with the code book, you might not be able to break it! I’ll bet you twenty pushups you can’t decode the coordinates, even after reading it cover to cover. Here are the coordinates for the next cache.” Sgt Stitches handed Lt Happy Camper the new coordinates:
DIGITAL FORTRESS
North Coordinates: ab cd.efg
98U983478RY93781aCR87Y3TJ827c4YbJSHT9374UR4H
873E28efgHMR3847HR94387HRJ984R387RWHM389HR79
SEL100572HSY0716d5SKD07
West Coordinates: abb cd.efg
c-dab-2feg2-0
Lt Happy Camper looked at the code for a moment, and then glanced disdainfully at the code book. Without even opening the book she scribbled down something on a piece of paper. “Unbreakable, huh? Are those the coordinates for the next cache?” She asked as she handed him the paper.
Sgt Stitches looked at the coordinates that Lt Happy Camper handed him. “Those are the coordinates, all right. But how did you know? I mean, you didn’t even read the code book!”
“It doesn’t matter how I figured it out… what matters is that you owe me some push ups. So, drop and give me twenty!”
July 2005: New container is a round Altoids tin. At replacement, cache contained a Santa Cruz County Geocoin.
