This BHO based trojan horse is not wide spread, but does exploit an unpatched vulnerability

Backdoor.Ryejet.B - Exploits an unpatched Jet DB vulnerability
http://www.symantec.com/avcenter/venc/data...r.ryejet.b.html

Backdoor.Ryejet.B is a back door Trojan horse that allows unauthorized remote access to a compromised computer. The Trojan is installed as a Browser Helper Object, and may be distributed embedded in a malformed .mdb file that exploits the Microsoft Jet Database Engine Malformed Database File Buffer Overflow Vulnerability (BID 12960).

Microsoft Jet Database Engine Malformed Database File Buffer Overflow Vulnerability
http://www.securityfocus.com/bid/12960