function IsValidURLProtocol(const URL: string): Boolean;
const
  Protocols: array[1..10] of string = (
    // Array of valid protocols - per RFC 1738
    'ftp://', 'http://', 'gopher://', 'mailto:', 'news:', 'nntp://',
    'telnet://', 'wais://', 'file://', 'prospero://'
  );
var
  I: Integer;   // loops thru known protocols
begin
  // Scan array of protocols checking for a match with start of given URL
  Result := False;
  for I := Low(Protocols) to High(Protocols) do
    if Pos(Protocols[I], SysUtils.LowerCase(URL)) = 1 then
    begin
      Result := True;
      Exit;
    end;
end;
//delphi/2263