Not many writers are plagiarists. All the same, most will have experienced the sudden anxiety, on formulating a sentence, that it has been written before. What if a phrase you encountered long ago has been lying dormant in your brain, only to reappear in the guise of original thought? Carl Jung observed this phenomenon in Man and His Symbols—and suggested that such "revelations" were a sign of genius. Modern-day law courts, however, tend to be less charitable: the "I didn't realise I was doing it" defence doesn't hold much water in intellectual property cases, which is fair enough, since the only person who actually knows is the accused. Still, the fact that the unconscious re-emergence of buried memories is unproveable doesn't mean the phenomenon doesn't exist. It even has a name, "crytomnesia," from the Greek kruptos (meaning hidden) and mneme (memory).
In the online world, where borrowings are endemic, a word like plagiarism, with its legalistic overtones (in Latin plagiare means "to steal"), is pretty useless. And so alternatives have emerged. One is "snarf"—taking a large document or file without the author's permission. ("Snarf" once referred to the practice of sniffing bicycle seats: how we got from one meaning to the other is a mystery.) Another is "abreticular"—used to describe a document created entirely by downloading other documents. This word is so new-fangled that it hasn't yet been accepted as part of the language—which makes it not a "neologism" but a "protologism."