Can't add bridged driver to extra network adapter in Win8.1

[shehaal]

Host: Windows 8.1 Pro
VirtualBox: 4.3.6 r91406
Guest: Windows 7 SP1 Pro x64
Guest Network Adapter 1: Bridged to host Ethernet adapter
Guest Network Adapter 2: Bridged to host WiFi adapter

I have an Optus 4G Huawei E3276 USB modem that installs itself as a network adapter in the host OS (unlike the Optus 3G Huawei E169 that installs as a dialup modem), which I need to add as a network adapter in VB for the guest OS to use. In the host OS, if I go to Control Panel > Network Connections, right click on the Optus 4G Mobile broadband connection and select Properties, I have the following:

Client for Microsoft Networks
File and Printer Sharing for Microsoft Networks
IPv6
IPv4

VirtualBox Bridged Networking Driver isn't listed for this connection, however when I installed VB it was automatically added for the Ethernet and WiFi adapters. If I try to add the driver as a network service (Install > Service > Have Disk, find VBoxNetFlt.inf under C:\Program Files\Oracle\VirtualBox\drivers\network\netflt), the list of network services found in VBoxNetFlt.inf is blank (see attached). It appears to be the same driver file used for the Ethernet and WiFi adapters, so I'm not sure why I can't add it to this. Does anyone have any idea why this isn't working?

Thanks!

[mpack]

A modem isn't a NIC. The VirtualBox installer looks for NICs and inserts the bridge mode redirection filter into the driver stack for that NIC. I don't know what the driver stack for your modem looks like, but I'm guessing it doesn't look like a normal NIC, however it appears to the user.