Public Service Announcement: if you get an email telling you that if you forward this message to five people you'll get a free flight from London to Asia courtesy of British Airways, DON'T BELIEVE IT. Versions of this hoax have been going around for years, involving Microsoft and Nike, among others. The premise of the hoax is always that these companies have some way of tracking email in order to determine who is forwarding their email. This, of course, is absolute nonsense.