Most ISP's that use Apache have set up
their domains as virtual hosts in their Apache configuration file
(httpd.conf). By default, Apache logs everything to access_log and
error_log (and perhaps access_log-ssl and error_log-ssl if you use
mod_ssl). In order to properly analyze log files for your ISP's clients
it is necessary to add a CustomLog directive within each virtualhost
creating a separate log file for each domain. Take my domain for
example: