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Microsoft Excel Code Execution (CVE-2009-0238):
Microsoft Excel contains a programming error that may allow a remote attacker to execute code on a vulnerable system. The problem occurs when Excel attempts to process a specially crafted document with an invalid object.
This issue is being actively exploited by Trojan.Mdropper.AC.
Details are available here: http://www.snort.org/vrt/advisories/vrt-rules-2009-02-27.html