JS/Downloader.gen - JavaScript Downloader Malware

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∟PWS (Password Stealer) Trojan Infection Removal

∟JS/Downloader.gen - JavaScript Downloader Malware

This section describes a real case where a JavaScript download malware was partially detected by McAfee VirusScan on a Windows XP system. The Trojan downloader successfully downloaded and executed a PWS Trojan installer program.

A couple of weeks ago, my computer got infected by a Trojan after visiting a .cn Website. Since I have McAfee VirusScan running on my Windows XP system. So I reviewed the McAfee OnAccessScanLog.txt log file as the first step to find out how this Trojan infected by computer.

In the OnAccessScanLog.txt, I found a section of records indicating a PWS Trojan infection happened on my computer. The infection started with a malicious JavaScript code as shown by these log record:

...
10/26/2008 5:58:21 PM Deleted hyang C:\Program Files\Internet Explorer
   \IEXPLORE.EXE C:\Documents and Settings\hyang\Local Settings
   \Temporary Internet Files\Content.IE5\UVQLMT01\ilink[1].htm
   \000000a0.js JS/Downloader.gen (Trojan)

10/26/2008 6:58:24 PM Script execution blocked hyang IEXPLORE.EXE
   (http://x.x.cn/swf/fx.htm) Script executed by IEXPLORE.EXE
   JS/Downloader.gen (Trojan)

10/26/2008 6:01:07 PM Deleted hyang C:\WINDOWS\system32\heb.exe
   C:\WINDOWS\SYSTEM32\PCAXYOQRXA.EXE PWS-Mmorpg.gen (Trojan)
...

I did a search on Google with JS/TrojanDownloader.gen, and learned that JS/TrojanDownloader.gen is a family of Trojan scripts written in JavaScript language. When executed, a JS/TrojanDownloader.gen script will connect to the Internet, download and execute another malware program on my computer.

According to the log file, McAfee VirusScan seems to deleted the JavaScript file and blocked the script execution initiated by the IE browser. But somehow, the PWS Trojan installer program, heb.exe, was downloaded and executed on my computer.

There are only two scenarios for what happened: (1). McAfee VirusScan did not really delete the Trojan downloader and did not really block the execution of the Trojan downloader; (2). The malicious Web page from .cn contains multiple Trojan downloaders. Some of them were too new for McAfee VirusScan to detect and delete. I have no way to confirm which scenario was really happened.

Conclusion, VirusScan did not a good job to fully protecting this computer against this Trojan JavaScript downloader. Read sections below to see what the PWS Trojan installer, heb.exe, did on this computer.