后门程序中，浏览远程主机的文件系统，已经下载指定文件，数据结构的设计和多线程传输和下载注定它的延时小。程序分了客户端和服务器端。-Backdoor programs, browse the remote host' s file system, have downloaded the specified file, data structure design and multi-threaded transfer and download a small delay bound to it