last I checked VNC is not
a secure protocol; If one of your clients suggests that is it, my GUESS is that it is sending it over ssh, etc.
FreeNX is a pretty easy to use solution for secure remote desktop access between windows and linux.
Even easier is using Hamachi (aka LogMeIn) to create a VPN between computers, then use standard KDE tools (krdc)
for remote desktop access between computers.. just make a note of the hamachi IP on the work machine before you go home. The nice thing about this option is you can use Samba/CIFS to access your remote data as if it was local (if you don't want/need the full remote desktop solution).
..both are in our repos, and also have windows clients available from their respective web sites.