The most common form of computer crime is vandalism with the objective of destroying a system or making it inoperable. Information theft, usually in the form of valuable computer programs, and the use of computers for personal benefit are also frequent offenses. Furthermore, criminals can steal merchandise by placing large orders by computer, or manipulate a computer system to create fictitious assets and earnings. Various stages in a computer operation are particularly vulnerable. During the data input phase, felons can introduce false data, alter data, remove key input documents, and fabricate false accounts and credits. During the programming stage, they can alter or steal programs. The central processing unit is especially vulnerable since its destruction can cripple a firm that has computerized the bulk of its paperwork. Data can be stolen during the output phase, and the communication of computer data through telephone circuits is open to electronic penetration. Computer security experts suggest systems be kept under guard and isolated from the other divisions of a firm. Also, programmers should not be allowed to operate computers; employees should have computer access for only limited periods of time; and access should be on a need-to-know basis only. Prosecution of computer crimes requires the use of computer generated evidence. However, present legal restrictions on such court evidence in the United States and Great Britain may make prosecution difficult. These restrictions are reviewed. Footnotes with references are included.