.DS_Store (or Desktop Services Store) is a hidden file created by OS X. Your Mac places a .DS_Store file into every folder you have opened, automatically. If you suddenly see .DS_Store files (and unable to get rid of it), you probably accidently activated the Show All Files. You can delete them, but it will be re-created again. Here is how you can make this file hidden again:
1.Launch Terminal by selecting Applications > Utilities
2.Enter the following command:
defaults write com.apple.finder AppleShowAllFiles -boolean false;killall Finder
3.Hit return, the Finder will restart and .DS_Store files (an other invisible files) will be hidden again.