Mac OS X is automatically creating .DS_Store file as soon as you’re working on some network drives. This is used to store some custom attributes.

If you want to prevent the OS to create those files automatically, follow the steps below:

• Open up a Terminal
• Run this command
  defaults write com.apple.desktopservices DSDontWriteNetworkStores true
• Restart your Mac

Once this is executed, the DS_Store files will only be created on local drives.