Have you ever plugged in a USB drive from a Mac into a Windows system and seen this:

Apple Double Files

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.