Does anyone know what the file ~/Library/Preferences/com.npvdata.client is for? I had a heck of a time with the file ~/Library/Preferences/com.npvdata.client.  Looked like it was some kind of cryptographic key file, and when I went to edit it, not only could I not change it, but also while I was editing it the file com.npvdata.client.swp and com.npvdata.client~ showed up, even though I was editing it in vi which doesn't create backup files.  I had a really hard time deleting it, too. 

I'm guessing this is part of some kind of copy protection or licensing scheme, but I'd like to know for sure where it is from, what it is for, and what danger there is, if any, of someone else getting a hold of it.
If my Googling-fu is stronger than yours, this appears to be linked to the Viscosity VPN client.
According to Viscosity technical support, Viscosity stores registration and trial information in this file, however it can be safely deleted if needed.