WinPcap is an open source freeware that acts as a library for packet capture and network analysis specifically for Win32. The WinPcap 4.1 version has been modified to enable generation of PDB files, compilation warning level is raised to /W4 for packet.dll and wanpacket.dll, support for AirPcapWrite into packet.dll and initial support for the NpfIm capture engine into packet.dll. These are the major changes. Bugs like the memory leaks in packet.dll when dealing with AirPcap adapters, several ancillary packet.dll APIs that were crashing when used with AirPcap adapters, fixed many warnings and a few bugs in the UserLevelBridge sample.