You protect your map with guedit, proedit, scmtoolkit, starforge, and other programs like that. After that, you can distribute your map and people can download it over Battle.net. People can play your map over Starcraft, but when they try to open it in Staredit, it will pop up a screen displaying a message that the map did not open due to some invalid stuff.
That means your map is protected and nobody will be able to open the map and fiddle around with it.
(SHHHH, people, don't tell this "newb" the "other stuff")