fun.html definition, relationships, removal:

The fun.html file is an essential part of a particular parasite and therefore is responsible for the pest's malicious activity. Exact purposes of fun.html depend on the related parasite's type and carried payload. Some threats can use fun.html 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 fun.html file is installed and used by trojan Avid Trojan.
In some cases a presence of fun.html 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 fun.html file using you regular spyware remover or antivirus program.