Prevalent in the 1980s due to lax security was the process of `dumpster diving'. A curious hacker or malicious cracker would search in the dumpsters of major corporations for thrown-out manuals, passwords, credit card numbers, et cetera.
When corporations became aware of the need for increased security (in the early 1990s), sensitive documents were shredded before being placed in dumpsters.
The term is also used for the retrieving of useful items (not necessarily computer-related) from dumpsters. Dumpster diving is illegal in the United States, though the laws on this do not seem to be very vigourously enforced.