Computer Viruses

Computer viruses cannot spread by infecting pure data; pure data files are not executed. However, some data, such as files with spreadsheet input or text files for editing, may be interpreted by application programs. Under these circumstances, the data files are “executed” and may spread a virus. Data files may also contain “hidden” code that is executed when the file is used by an application, and this too may be infected. Technically speaking, however, pure data itself cannot be infected by computer viruses.
The first definition of a computer virus was provided by Dr. Frederic B. Cohen who defined a virus as “A computer program able to infect other programs by modifying them to include a possibly evolved version of itself.” Although Dr. Cohen and others have attempted formal definitions of computer viruses, none have gained widespread acceptance or use. Dr. Cohen’s definition includes any program capable of self-replication. Thus, by his definition, programs s...