I observed a user accused of plagiarism a few minutes ago for quoting copied text from the Internet without citing the source. Now here's my question: Is quoting not enough proof that the Op never intended to pass off someone else's work as his own? Please educate me.
Personally, I think it is plagiarism, because you really need to give credit for what you are quoting. But I understand this might be polemic and not everyone agrees.
Being more practical, I know there is (or at least there was) a bot that crawled the forum posts looking for plagiarism. I think this bot might catch this kind of user and ban him.
If you want to do things right, quote everything you copied from internet and give the appropriate credit. In my opinion this is a very basic etiquete for internet.