It's contingent on a Google referrer. They should be removed from the index.

Compare these:

  curl -e http://www.experts-exchange.com/OS/Microsoft_Operating_Systems/Windows/XP/Q_21692879.html?qid=21692879 > without_google.html

  curl -e http://www.google.com http://www.experts-exchange.com/OS/Microsoft_Operating_Systems/Windows/XP/Q_21692879.html?qid=21692879 > with_google.html