Dictionary.net

/dump'-ster di:'-ving/ 1. The practice of sifting refuse froman office or technical installation to extract confidentialdata, especially security-compromising information ("dumpster"is an Americanism for what is elsewhere called a "skip").Back in AT&T's monopoly days, before paper shredders becamecommon office equipment, phone phreaks (see phreaking) usedto organise regular dumpster runs against phone company plantsand offices. Discarded and damaged copies of AT&T internalmanuals taught them much. The technique is still rumored tobe a favourite of crackers operating against careless targets.2. The practice of raiding the dumpsters behind buildingswhere producers and/or consumers of high-tech equipment arelocated, with the expectation (usually justified) of findingdiscarded but still-valuable equipment to be nursed back tohealth in some hacker's den. Experienced dumpster-divers notinfrequently accumulate basements full of moldering (but stillpotentially useful) cruft.