The TROJ_MDROPPER family became one of the most prominent malware in 2006 because of its penchant for exploiting unpatched vulnerabilities in Microsoft Office applications. This year, this family is making a comeback. It started making rounds again late January with TROJ_MDROPPER.EQ, which exploits a flaw in MS Word.

This time, Trend Micro has detected TROJ_MDROPPER.FC, which takes advantage of yet another vulnerability in MS Office. When run, it drops and executes a Trojan detected as TROJ_AGENT.LEO.

Microsoft has already released another Security Advisory regarding the mentioned vulnerability. While the exploit primarily targets MS Excel, other Office applications may be targeted. Thus users, are advised not to open Office files (.DOC, .XLS) from untrusted or unexpected sources, especially since a security patch is yet to be released.