Are you waiting to finish your book before you release your words to the public? If you're like 90% of the people I meet, you're probably saying, "I need to copyright it first. " If so, take my word, no one is going to make a fortune from an excerpted passage. But if you're still bothered, just type Copyright (c) 2013 by (your name) at the bottom of everything you write on the web. It will hold up in a court of law.
Moving on, so now that you have peace let's remember why you write in the first place. It's is to change the world. You may not have that idea but the fact is words change ideas, ideas change actions, actions change cultures, and cultures change the world.
Don't hide your words for the big pay day. The big pay day will come as a result of your liberality.