HOWTO: Make Virtual WiFi work in Windows 7 for MacBook Air (Late 2010)

Question

I just spent several hours figuring out what is a bug in the Broadcom WiFi drivers for my new MacBook Air, and thought I would post how I fixed it for others until Apple can get Broadcom to fix their drivers.
Virtual WiFi:
First, what is Virtual WiFi. Virtual WiFi is a feature in Windows 7 that allows a single WiFi adapter in a computer to look like more than one adapter. The most common use for this is for software like Connectify that allows you to use your laptop as a wireless access point (AP) when you travel. For example, you might settle into a hotel room, pay for an Internet connection for your MacBook, and then want to share that connection with your iPhone, iPad, and other devices. For Virtual WiFi to work, the WiFi drivers for your WiFi hardware need to indicate that they support the feature, and then in Device Manager in Windows Control Panel, under Network Adapters you will see the "Microsoft Virtual WiFi Miniport Adapter" listed. Notably, this adapter was missing after installing Windows 7 and BootCamp 3.1 on my MacBook Air (Late 2010).
Why it Doesn't Work:
The strange thing is, this was working fine on my wife's MacBook from 2008, with similar Broadcom WiFi hardware. It turns out that whoever made the Broadcom driver file made a small copy-and-paste error, and neglected to support Virtual WiFi for the slightly different chip that is in the MacBook Air versus the MacBook. By fixing the driver file, the issue can be fixed. The problem is right here in the file, which we'll get to more below:
%BCM430N_DeviceDesc% = BCM43XNM_NT61, PCI\VEN14E4&DEV432b
%BCM430N_DeviceDesc% = BCM43XNG_NT61, PCI\VEN14E4&DEV432c
%BCM430N_DeviceDesc% = BCM43XNM_NT60, PCI\VEN14E4&DEV4353
My wife's MacBook uses the first line with DEV_432b at the end. Note that it uses the installation section BCM43XNM_NT61 which refers to Windows 7 and correctly installs Virtual WiFi. The newest MacBook Air uses the last line with DEV_4353 at the end (a slightly different chip). Note that it incorrectly refers to the installation section BCM43XNM_NT60, which is Windows Vista with no support for Virtual WiFi.
How to Fix It:
1) You first need to extract the Broadcom drivers that are in the latest version of BootCamp so that you can modify the INF file. To do this, I followed all of the instructions in the BootCamp Assistant from Mac OS X on my MacBook Air to download the WindowsSupport folder with BootCamp drivers, which you can save to the hard drive or burn to a CD. Once you have this, open the folder "Boot Camp\Drivers\Broadcom". We need to extract the file BroadcomNetworkAdapterWin7_32.exe or BroadcomNetworkAdapterWin7_64.exe depending on whether you are using a 32-bit or 64-bit version of Windows 7. I was able to do this with WinRAR installed, by right-clicking and selecting to extract the file to a folder.
2) In the folder from the last step, there are 31 files on my installation, but the one we want is bcmwl6.inf. If you open that file the first two sections (BROADCOM.NTamd64.6.1 and BROADCOM.NTx86.6.1) are the ones with the error as reproduced above. The first section is for 64-bit installations, and the second section is for 32-bit installations.
3) Modify the last line of each section to change BCM43XNM_NT60 to BCM43XNM_NT61, and save the file.
4) Now we need to install the driver from this folder onto the MacBook Air. I did this by opening Device Manager from Control Panel, right-clicking the "Broadcom 802.11n Network Adapter" under Network Adapters, and selecting "Uninstall" followed by "Update Driver Software". Point the update dialog to the folder where you modified the driver, and let it install.
5) Note that because the INF file is modified the driver is no longer correctly signed. You will see a warning to this effect, and you should select to install the driver anyway.
6) You should now see the "Microsoft Virtual WiFi Miniport Adapter" in Device Manager, and software like Connectify should work to share your WiFi connection.
Hopefully Apple will fix this the correct way soon, by getting Broadcom to fix their driver and updating BootCamp to include it. At the time of this writing, the Broadcom driver version is 5.100.57.8 so anything later than that may be fixed.
Good Luck!

Answer 1

That is one heck of a post for a newcomer here. Your instructions worked like a charm, with one exception:
When uninstalling the Broadcom Device, I had to check the box to delete the driver, and then had to scan for new hardware to get the device to show back up. Then I was able to load the edited driver software.
I am not complaining, but very grateful, as I was pulling my hair out on this one.