Microsoft Internet Explorer 5.22, and other 5 through 6 SP1 versions, sends Referer headers containing https:// URLs in requests for http:// URLs, which allows remote attackers to obtain potentially sensitive information by reading Referer log data.
http://www.securityfocus.com/bid/9295
http://www.securityfocus.com/archive/1/348574
http://www.securityfocus.com/archive/1/348360
http://www.gadgetopia.com/2003/12/23/OutlookWebAccessPrivacyHole.html