The Trojan downloader (download-aag AKA Pgpcoder) exploits a well-known Internet Explorer vulnerability (MS04-023) to download hostile code onto vulnerable Windows boxes. It then searches for files with various extensions and encodes them. The original documents are deleted and the newly encoded files become unreadable. The malware also drops a message onto the system with instructions on how to buy the tool needed to decode the files, demanding payment of $200 from victims if they ever want to see their documents again.