Every time I delete it from the desktop, I get the same file ".DS_store" created after some time. Is there a reason why this happens ? And can I permanently stop it from being created ?
Type this in Terminal (/Applications/Utilities/Terminal.app):
The first command sets the hidden files visibility to hidden; the second one forces Finder to restart, action that is needed in order to make it take in consideration the previous command.
You can also log out/reboot instead of killing the Finder, but the first command is needed to change a hidden preference (one that the Finder can’t change using the normal Finder view options or preferences).