CheckReferer Function will make sure that the URL that has referred your ASP page, is in your list of allowed URL's. This is useful for Form submission, so you can ensure that only YOUR form scripts are the ones posting to your asp scripts, no hackers.

bool = CheckReferer(ValidReferers)

Argument:
ValidReferers: one or a list of valid referer addresses
separated by comma and without http:// or /

<%
If CheckReferer("www.livio.net,www.lasp.net") Then
  '--- the URL is ok - do rest of processing
Else
  '--- referring url is bad. Spit out an error message
End If
%>

<%
Function CheckReferer(ValidReferers)
   dim arURLs, tmpCount, boolValidURL
   dim strURL, nIndex
   If InStr(ValidReferers, ",") > 0 Then 
     arURLs = Split(ValidReferers, ",") 
   End if
    boolValidURL = False
    strURL = Request.ServerVariables("HTTP_REFERER")
   If LCase(Left(strURL,7)) = "http://" Then strURL = Mid(strURL,8) End if
   If LCase(Left(strURL,8)) = "https://" Then strURL = Mid(strURL,9) End if
    nIndex = InStr( strURL, "/")
   If nIndex > 0 Then strURL = Left(strURL,nIndex-1) End if
   If IsArray(arUrls) Then
     For tmpCount = 0 To UBound(arURLs)
       If strURL = arURLs(tmpCount) Then boolValidURL = True End if
     Next
   Else
     If strURL = ValidReferers Then boolValidURL = True End if
   End if
    CheckReferer = boolValidURL
End Function
%>