UnrealIRCd 3.2.8.1, as distributed on certain mirror sites from November 2009 through June 2010, contains an externally introduced modification (Trojan Horse) in the DEBUG3_DOLOG_SYSTEM macro, which allows remote attackers to execute arbitrary commands.
http://www.vupen.com/english/advisories/2010/1437
http://www.unrealircd.com/txt/unrealsecadvisory.20100612.txt
http://www.openwall.com/lists/oss-security/2010/06/14/11
http://www.exploit-db.com/exploits/13853
http://security.gentoo.org/glsa/glsa-201006-21.xml
http://secunia.com/advisories/40169
http://seclists.org/fulldisclosure/2010/Jun/284