A message is provided to a tracking server system in response to a client system referencing a predetermined resource locator that corresponds to a resource external to the tracking server system. The tracking server system indirectly provides for the client system to have an informational element selectable...http://www.google.com.hk/patents/US6189030?utm_source=gb-gplus-share專利 US6189030 - Method and apparatus for redirection of server external hyper-link references
