Ask HN: Hackers - mediocre programmers?

My software Engineering lecturer was taking us through some types of Software Engineering methodologies. On one end of the spectrum was the Milestone plan-driven model, and the on the other were the Hackers. He told us that hackers produce crappy software with no documentation whatsoever, while I believe its the opposite case(Linux, the Internet etc ) How would you explain to such a person who hackers really are, and what they do?