Format string vulnerability in the NSRunAlertPanel function in eBay Skype for Mac 1.5.*.79 and earlier allows remote attackers to cause a denial of service (application crash) and possibly execute arbitrary code via a malformed Skype URL, as originally reported to involve a null dereference.
http://www.vupen.com/english/advisories/2006/3895
http://www.skype.com/security/skype-sb-2006-002.html
http://www.securityfocus.com/bid/20218
http://www.security-protocols.com/modules.php?name=News&file=article&sid=3259
http://www.kb.cert.org/vuls/id/202604
http://securitytracker.com/id?1016966