判断文件类型（文件的真正类型，不是根据扩展名判断）,通过文件头来判断

bool xx=false; //default sFileName is not Exe or Dll File

System.IO.FileStream fs=new System.IO.FileStream(sFileName,System.IO.FileMode.Open,System.IO.FileAccess.Read);

System.IO.BinaryReader r=new System.IO.BinaryReader(fs);

string bx="";

byte buffer;

try

{

buffer=r.ReadByte();

bx=buffer.ToString();

buffer=r.ReadByte();

bx+=buffer.ToString();

}

catch (Exception exc)

{

Console.WriteLine(exc.Message);

}

r.Close();

fs.Close();

if (bx=="7790"||bx=="8297"||bx=="8075")//7790:exe,8297:rar,8075:pk

{

xx=true;

}

Console.WriteLine(bx);

return xx;

                dll:MZ
                exe:MZ
                rar:Rar
                zip:PK