When IE is configured to access internet using proxy, the user’s authentication details are cached locally without IE prompting the user. Even though the ‘save my password’ option is not checked, the user’s proxy authentication details are cached locally without the user’s knowledge.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/35307/ieCache.txt
Source: https://packetstormsecurity.com/files/35307/ieCache.txt.html