From MIXXnet Wiki
HostServ is a MIXXnet service that gives users a generic vhost to hide their real IP address/hostname. The generic free vhost is in the form of: "registerednick.users.mixxnet.net". We do not currently provide custom vhosts except in very special cases.
To activate your generic vhost: /msg hostserv generic assign
Syntax: /msg HostServ ON
Activates the vhost currently assigned to the nick in use. When you use this command, any user who performs a /whois on you will see the vhost instead of your real IP address.
Syntax: /msg HostServ OFF
Deactivates the vhost currently assigned to the nick in use. When you use this command any user who performs a /whois on you will see your real IP address.
Syntax: /msg HostServ GROUP
This command allows users to set the vhost of their CURRENT nick to be the vhost for all nicks in the same group.
Assigns a generic vhost to your nickname.
Removes your generic vhost and restores your normal hostname.