asp.net 实现防迅雷等下载工具盗链

public void ProcessRequest(HttpContext context) 
{ 
context.Response.ContentType = "application/octet-stream"; 
HttpRequest req = context.Request; 
string filename = req.Url.AbsolutePath; 
string userid = string.Empty; 
if (HttpContext.Current.Request.Cookies != null && HttpContext.Current.Request.Cookies["userid"] != null) 
{ 
userid = HttpContext.Current.Request.Cookies["userid"].Value; 
} 
if (userid == "1") 
{ 
string uuu = context.Server.MapPath(filename); 
context.Response.TransmitFile(uuu); 
} 
else 
{ 
string u2 = context.Server.MapPath("default.rar"); 
context.Response.WriteFile(u2); 
} 
}