Information as a "lethal weapon"...

What I learned today, whatever you post on the internet (i.e. blog), information is stored somewhere. I'd like to know where? As mentioned in class, isn't that an act against one's privacy? I also noticed that facebook has even pointed out that anyone can search our site by free texting on the internet, that's kinda scary. Social networking as information that can be "potentially harmful?" hmm.. makes you think twice about what to post, what is out there, and who could be tracking you down???