Multiple unspecified scripts in mIRC allow user-assisted remote attackers to execute arbitrary code via the '|' (pipe) shell metacharacter in the name of the song in a .mp3 file.
http://www.securityfocus.com/archive/1/476649/100/0/threaded
http://www.securityfocus.com/archive/1/476283/100/0/threaded
http://wouter.coekaerts.be/site/security/nowplaying
http://securityreason.com/securityalert/3036
http://secunia.com/advisories/26491
http://lists.grok.org.uk/pipermail/full-disclosure/2007-August/065227.html