Just back from a seminar on "Trends and Strategic Issues for Libraries in Global Information Society". We got printed proceedings of the seminar. While going through this proceedings, one paragraph looked very familiar to me. Oh, we had written it only few months back to report a group discussion on open access. This report, we made widely available over net through various discussion forums. We had also archived it in our repository. This familiar looking paragraph was included in a paper. I quickly jumped to reference section of the paper to see if we are lucky to get a citation. In vain, I should have remembered that people, who plagiarize, don't mention their actual source. It is their trade secret so won't even mention indirectly. For them, references are mere formality, so they will cite sources which they might have not even seen before.
But why get got? There are number of softwares for rewriting articles. Just have a look at "The best article rewriting software on earth". It mentions about software tools which will rewrite for you. Simply paste the text and you will get new text different from the original. These includes WordFlood 2.0, Content Rewriter Pro and Essay Town. Some payment may be required to get fully functional versions. With the help of these tools one can rewrite articles and hope to escape being caught by search engines like Google. However, do you know the best software? No prize for guessing it right, it is our brain. One can definitely use tools along with brain. WordWeb could be of great help. It is a small free utility to serve as English thesaurus as well as a dictionary.
There are no copyrights on ideas. Only well documented innovations are protected through patents. But coping ideas' written expressions as such without acknowledging the original authors is called plagiarism. It does not go well in academics when someone is trying to project others' idea as one's own. Punishment is mostly in form of bad reputation among peers and negative employer's assessment. Better would to express the idea in one's own words. Tools can help you if you are at lost for better words. Importantly, it won't cost anything if you cite the original author. At the most you will have to add more line in your word processor.
It is always a bad idea to plagiarize Open Access material because everybody knows about it. Being openly accessible, such material is widely indexed by Internet search engines. It will always show up. Modern search engines are designed in a fashion to understand which one is original and which one is plagiarized.