Troj_MSJet.Y is the Trend Micro detection for a specially crafted .MDB file that attempts to exploit a vulnerability in Microsoft Jet Database Engine (Jet) that could allow remote code execution.

More information about the said vulnerability can be found in the following link:

http://www.microsoft.com/technet/security/advisory/950627.mspx

Once successfully exploited, the said vulnerability could allow this Trojan to drop and execute an .EXE file detected by Trend Micro as TROJ_AGENT.CG. As a result, routines of the dropped file may be exhibited on the affected machine.

More information can be found at this Trend Micro page.