Here is some advice.
If you're applying for a job, and the application process includes a written exercise, do not plagiarize your written exercise from materials you find online.
And then, when the person reviewing your exercise points out to you that entire paragraphs are word-for-word the same as what can be found online, do not try to assure her that it's somehow just coincidence.
I had a candidate do this today. It's the second time I've caught someone in this, and I have to wonder how many more I haven't caught.
Plagiarism = not a good idea. Not only is it, you know, wrong, but if you cheat your way into a job, how do you plan on keeping that job? The hiring process is designed to identify candidates who will excel in the position -- if you misrepresent your skills, you're likely to end up in a job that you aren't a good fit for and might get fired from.
So why do people do this? I suspect it's some combination of cockiness and laziness -- the belief that their own work would be just as good, but they just aren't inclined to put in the time to do it themselves.
I kind of wish we could print their names publicly, like the hiring equivalent of a sex offenders list.