PacketBuilder builder = new PacketBuilder(); builder.AddField("username", "johndoe"); builder.AddField("password", "secret123"); Packet packet = builder.Build(); networkConnection.Send(packet);In this example, the developer is using the PacketBuilder to create and send a packet with two custom fields: username and password. The PacketBuilder is used to add these fields and build the final packet, which is then sent over the network through the networkConnection object. It is difficult to determine the specific library used in this example without more context, as there are many networking libraries available for C#. However, some popular libraries for packet building and networking in C# include System.Net.Sockets and SharpPcap.