Understanding what plagiarism is and how to avoid it, could save you some trouble in the future. Even rewritten articles can fall under plagiarism, if not properly cited. A simple "cite" is very polite :).

Choosing the right words is very important in rewriting something without proper citation. It's usually safe to start out by saying something like, "I have read", or "on such and such site", but a mention should be included if it's not your original idea.