WNAD.DAT definition, relationships, removal:

The WNAD.DAT file is an essential part of a particular parasite and therefore is responsible for the pest's malicious activity. Exact purposes of WNAD.DAT depend on the related parasite's type and carried payload. Some threats can use WNAD.DAT 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 WNAD.DAT file is installed and used by adware WinAD.
In some cases a presence of WNAD.DAT does not mean that your system is infected. The file may actually belong to some fully legitimate applications and therefore must stay intact. If you are in doubt, please scan the WNAD.DAT file using you regular spyware remover or antivirus program.