Who Owns Information on the web?

Information on the web has become a free for all. People are posting information and people are taking information. Whether the information is accurate is something the user needs to determine and also be critical of. Information on the web often has pdf files to download which implies the author would like you to access it. Personally I feel comfortable using ideas from the internet but when I do several questions come to mind such as: What is the author's intent? Is the information valid? How much should I use before it becomes plagiarizing or cheating? Now, I know I will use information keeping in mind the author's purpose for posting the content and not take a part of it and use it out of context for my own personal gain. But there will be people who use the web information out of context, for commercial use, or for reasons other than the author's original intent. Now that I know more about Creative Commons, as a teacher I will make students aware what is out there that can be used and what is protected.