Sun Java System Identity Manager (IdM) 7.0 through 8.0 responds differently to failed use of the end-user question-based login feature depending on whether the user account exists, which allows remote attackers to enumerate valid usernames.
blogs.sun.com/security/entry/sun_alert_253267_sun_java
secunia.com/advisories/34380
securitytracker.com/id?1021881
sunsolve.sun.com/search/document.do?assetkey=1-21-137621-11-1
sunsolve.sun.com/search/document.do?assetkey=1-21-140936-01-1
sunsolve.sun.com/search/document.do?assetkey=1-66-253267-1
www.securityfocus.com/bid/34191
www.vupen.com/english/advisories/2009/0797