Some malware authors are still fond of using the good old techniques to spread their wares. One of these techniques is to send e-mail messages with "Security Updates", released by a well-known software vendor.
Today we received multiple reports about a message claiming to be a "Critical Security Update" from Microsoft. The message had a ZIP archive with a trojan downloader inside.
To become infected a user needs to extract the trojan's file and to run it. It should be noted that unlike Swen's message, this fake update message does not even look legitimate, so we're not going to see a lot of real infections.
A short description of the trojan and a screenshot of the spammed message can be found here.