Simple Users Online: Keep track of the users online in a database

This class is meant to keep track of the users currently accessing a site.

The class stores the unique IP addresses of each users online in a database. The class tries to determine the real IP address of uses behind proxy servers.

The class also performs the maintenance task of deleting all the records of user IP addresses that are stored before a given timeout period specified in a class variable.

The class count the number of user accessing the site by counting the number of unique user IP address records currently stored in the database.