QuickLook in Apple Mac OS X 10.6 before 10.6.7 allows remote attackers to execute arbitrary code or cause a denial of service (memory corruption and application crash) via an Excel spreadsheet with a crafted formula that uses unspecified opcodes.
http://support.apple.com/kb/HT4999
http://support.apple.com/kb/HT4581
http://lists.apple.com/archives/security-announce/2011/Mar/msg00006.html
http://lists.apple.com/archives/Security-announce/2011//Oct/msg00001.html
http://labs.idefense.com/intelligence/vulnerabilities/display.php?id=898