Unreal ircd versions below 3.2 suffer from a faulty cloaking scheme to hide IP addresses which allows attackers to find the true IP address of people using the server.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/33722/unreal.ircd.txt
Source: https://packetstormsecurity.com/files/33722/unreal.ircd.txt.html