There are many sources accessible through the internet or modem connections which contain information such as social security numbers, bank account information, credit card account numbers, passwords, and even credit histories. With this information, criminals can spend your money or impersonate you and it may be months before you even become aware something is wrong. Though each computer criminal will have their own reasons for breaking the law, there are several basic reasons why people choose to break the law. Obviously however, a gain of some type is going to be the first and foremost cause of computer crime. They may see a chance to alter or create their own financial records, change or create another person's records for a fee, or steal information for their own use.
Software piracy is probably the most common and over-looked computer crime.
However, you cannot rightfully say that all computer related crimes are initiated due to greed. Many 'hackers' will claim that they breach the security of computer systems for the thrill, satisfaction, and to impress their friends. If you manage to contact one of these hackers, they will probably claim that they are doing nothing illegal, though some will use the term 'semi-legal' if confronted. The truth, however will be based upon their actions and the state and federal laws which are broken.