Trojan-Downloader:W32/Agent.ACL

This Trojan usually arrives on the system as a dropped file of Trojan-Downloader:W32/Agent.EOA.However, this doesn't normally exists as a "physical" file since this malware's executable image is usually just injected into the iexplore process by Trojan-Downloader:W32/Agent.EOA. Running in the process context of Internet Explorer, this Trojan increases the chance of getting through the system firewall since it is most likely that Internet Explorer has already been included by the user to the list of approved applications that can pass through the firewall. To ensure only an instance of itself is running, it checks for the malware-created mutex "k4j.32H_f7z_Z6e.g8G0".The malware then retrieves the system's basic disk properties such as volume information, serial and volume type, the computer's IP address, and running antivirus processes that match its list. It then use this data as a parameter to an HTTP request to download a set of malware from a remote server.

Based on the characteristic being checked by the malware, the individual executable image included in the downloaded payload can either be dropped as a single file in computer's temporary folder and then executed as an independent process, or the image will be injected into a hidden Internet Explorer process space. As of current testing, the downloaded payload usually contains two executable images which are detected as:

• Rootkit:W32/Agent.Ey and Email-Worm:W32/Agent.BC