The other form of dumpster diving deals with deleted files that remain in the system. This form of computer crime is very easy to execute to anyone with computer knowledge who has access to the system. "Usually, "deleting" a file, a disk, or a tape doesn't actually delete data, but simply rewrites a header record. If you are running MS-DOS, for example, you can delete a file via the DEL command; however, someone can retrieve the contents of the file simply by running UNDELETE"(). Another factor that contributes to the ease of perpetrating this type of crime is the fact that most companies do not erase disks but instead write new data over old. Sometimes the new data may not be the same length as the old data and skilled computer criminals may find critical data that should have been erased. .
Another form of physical computer crimes is wiretapping. Many criminals use wiretapping as a way to eavesdrop on line of communications. Network wiring and telephone lines are usually not as secure as they should be in most corporations. This lack of security allows trespassers to physically damage a system as well as intercept data running through the wires. The largest problem with wiretapping is telephone fraud. "Telephone fraud has always been a problem among crackers, but with the increasing use of cellular phones, phone calling cards, and the ordering of merchandise over the phone using credit cards, this problem has increased dramatically in recent years"().
A third more technologically based computer crime is intercepting electronic emanations from computer equipment. This is called eavesdropping on emanations. Although this type of crime is usually committed against military and intelligence data, businesses and corporations should at least be aware of the risk that this crime presents. Criminals receive electronic impulses from computer equipment when a computer key is struck. These impulses are then monitored, intercepted, and decoded.