Secunia Security Advisory – Shalom Carmel has reported a weakness in OS/400, which can be exploited by malicious people to identify valid user accounts.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/37172/sa14964.txt
Source: https://packetstormsecurity.com/files/37172/Secunia-Security-Advisory-14964.html