add.php definition, relationships, removal:

The add.php file is an essential part of a particular parasite and therefore is responsible for the pest's malicious activity. Exact purposes of add.php depend on the related parasite's type and carried payload. Some threats can use add.php to serve annoying pop-up advertisements or store certain configuration settings, while others need it to corrupt files, steal user confidential information or run a spreading routine. In any case, DO NOT open this file!
The add.php file is installed and used by keylogger DSK Lite 1.0 and trojan PHP Logger.
Sometimes a presence of add.php does not indicate that your computer is infected. It can be an essential system file or a file installed by harmless legitimate software and therefore may not pose any threat to your privacy and the system. Although such cases are quite rare, you should thoroughly examine add.php before completely deleting or leaving it in the system.