A computer-based customer tracking system passively identifies customers. Acquired biometric identification information is sent to a computer processor, which searches files in a library for matching biometric data. If no match is found, the processor opens a new file in the library. If a match is found, said processor stores in the file that a repeat identification has occurred. If said processor is only able to reduce the number of possible matches to two or more files, personnel determines if a match certain has occurred. If prior activity information stored in the file exceeds a predetermined level, the prior activity information is retrieved from the file and sent to a terminal, preferably at the location of the transaction. New information from the transaction is stored for future access. The processor scans the files periodically, and deletes files which include activity level below a predetermined level over a preselected time period.