<p>There's been plagiarism for a long time. The internet has made it easier to plagiarize and easier to catch plagiarism.
I recall doing research for a paper in college and stumbling across two works: the first was a Ph.D. dissertation. The second one was a published monograph by a different author. The monograph was a verbatim copy of the dissertation. They happened to be side by side on the library shelf (which is why I picked both). Whoever catalogued the two works had never bothered to read them.
One of of LBJ's appointments, a university president, turned out to have plagiarized. But it took a long time for his sin to catch up with him. </p>
<p>I suspect many a prof shows a student's paper to a colleague to ask the colleague's opinion. Sometimes, it's to show how impressive a paper is; sometimes, it is to ask a second opinion about grading; and sometimes, it is to share one's suspicion that the paper was plagiarized or bought wholesale from someone else. The internet has created virtual communities of people who share their thoughts with people they hae never met (like CC!). But without the internet, such sharing occurs anyway.</p>