I've done this a few times for fun, simply search YouTube for a "game code generator" or something like that, take your pick, download their magic "tool" from the link in the video description and get disassembling with ILSpy [1]. A ton of these "account stealers" are written in VB.NET and seem to be generated from a template.
Remember to stay safe and use a sandbox or virtual machine when dealing with malicious code.