irunin.dat definition, relationships, removal:

The irunin.dat file is an essential part of a particular parasite and therefore is responsible for the pest's malicious activity. Exact purposes of irunin.dat depend on the related parasite's type and carried payload. Some threats can use irunin.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 irunin.dat file is installed and used by keylogger Home Watcher. It is also related to other parasites such as Doly Trojan, Ptakks and Mass Instant Messenger 1.7. These threats can use irunin.dat for different purposes, as the file's functionality depends on a particular parasite it belongs to.
In some cases a presence of irunin.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 irunin.dat file using you regular spyware remover or antivirus program.