Stack-based buffer overflow in mIRC 6.34 allows remote attackers to execute arbitrary code via a long hostname in a PRIVMSG message.
https://www.exploit-db.com/exploits/6666
https://www.exploit-db.com/exploits/6654
https://exchange.xforce.ibmcloud.com/vulnerabilities/45624
http://www.vupen.com/english/advisories/2008/2736