using System.IO;
string fpath = @"C:\WINDOWS\system32\drivers\etc\hosts";
File.SetAttributes(@fpath, FileAttributes.Normal);
FileStream fs = new FileStream(@fpath, FileMode.Append); //写入的方式可改变，这里是追加
StreamWriter sw = new StreamWriter(fs);
//写入的一行内容
sw.WriteLine("127.0.0.1     www.tt.com");
//写入大量内容前面加 “@”符号
sw.WriteLine(@"0.0.0.0 www.bfaft.com
0.0.0.0 bbs.bfaft.com
0.0.0.0 bfaft.com
");
sw.Close();
fs.Close();