Have you ever plugged in a USB drive from a Mac into a Windows system and seen this:
Well, congratulations! You have Mac “Cooties”. I hope your shots are up-to-date!
What are these files any way? On an OS X system the Spotlight feature indexes a lot of metadata, and I mean a lot. This works all fine and well on an HFS volume but if you copy a file onto a FAT volume, most commonly seen in USB drives, it does not work so well. OS X does not want to simply throw out all this precious metadata so it creates the “.Spotlight-v100” and “.fseventsd” files in order to preserve it. These file remain in a deep cryogenic freeze until you take the Mac Cooties USB and plug it into a different Mac. The new OS X system will recognize these files and use them to build the metadata back up in Spotlight.
Mac Cooties is also a great indicator that a system has been plugged into a Mac. Remember this during any triage process of loose media.
If you want to know more about the “.Trashes” files check out one of my previous posts: The Tale of Two Trashes.
If you are looking for more technical details check out the wikipedia entry for Apple Double Files. A word of advice though, this type of detail is fine among the tech crowd. However, I have found that when I need to explain the existence of these files to a non-technical person the Mac Cooties story seems to go over better. Just my thoughts anyway.