Differentiate VMware network adapter from physical network adapters -or- Detect Virtual Network Adaptor
The beginning (first 3 segments) of the mac address shows if a interface is virtual:
"00:05:69"; //vmware1
"00:0C:29"; //vmware2
"00:50:56"; //vmware3
"00:1C:42"; //parallels1
"00:03:FF"; //microsoft virtual pc
"00:0F:4B"; //virtual iron 4
"00:16:3E"; //red hat xen , oracle vm , xen source, novell xen
"08:00:27"; //virtualbox
EDIT
To be more clear, if a interface has a MAC address that starts with any of the above given strings, then it's virtual.
I found a site to get more complete list of MAC address prefix, after reading clyfe answer.
Please visit: Vendor/Ethernet/Bluetooth MAC Address Lookup and Search
For example: VirtualBox has 17 MAC prefix!
Prefix Vendor
000F4B Virtual Iron Software, Inc. (was: Katana Technology)
001307 Paravirtual Corporation (was: Accenia, Inc.)
0013BE Virtual Conexions
0021F6 Virtual Iron Software
00240B Virtual Computer Inc.
00A0B1 First Virtual Corporation
00E0C8 virtual access, ltd.
545200 linux kernal virtual machine (kvm)
000F4B Virtual Iron Software, Inc. (was: Katana Technology)
001307 Paravirtual Corporation (was: Accenia, Inc.)
0013BE Virtual Conexions
0021F6 Oracle Corporation (was: Virtual Iron Software)
00240B Virtual Computer Inc.
00A0B1 First Virtual Corporation
00E0C8 virtual access, ltd.
18922C Virtual Instruments
3CF392 Virtualtek. Co. Ltd
At the end I preferred to detect Virtual network adapter from its 'Network Card Description'. If I see 'Virtual' or 'VMWare' word in it description (C++: IP_ADAPTER_INFO::Description), I will assume it is virtual network adapter.