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F-Secure Malware Information Pages: Trojan-Downloader:W32/Agent.BRK
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Summary
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| Trojan-Downloader:W32/Agent.BRK attempts to download and install other malware onto the affected system. |
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Disinfection
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Detection and Disinfection of Rootkits
If the rootkit is not detected or it is hidden that FSAV cannot detect its file, it is still possible to detect the malicious activity by scanning the system with generic rootkit scanner, such as F-Secure BlackLight. More information about F-Secure BlackLight Rootkit Elimination Technology can be found here:
http://www.f-secure.com/blacklight/
The BlackLight utility is also able to disinfect computers that are infected by rootkits.
Automatic Disinfection
Usually standalone malware (backdoors, worms, trojans, etc.) is automatically removed by F-Secure Anti-Virus (FSAV) starting from version 5.40. Malware files get automatically renamed by FSAV, so they can not be started any more. In some rare cases, when automatic disinfection is not possible, a user can select disinfection action by him/herself to make FSAV rename or delete an infected file. In some special cases, it is recommended to use specific disinfection tools provided by F-Secure. They can be downloaded from our ftp site:
ftp://ftp.f-secure.com/anti-virus/tools/
F-Secure Anti-Virus can be purchased from our web shop or from our authorized distributors. A trial version F-Secure Anti-Virus, limited to 30 days, can be downloaded from our website:
http://www.f-secure.com/download-purchase/
All the latest versions of FSAV can download anti-virus database updates automatically. However, these updates can be also downloaded and installed manually from our web or ftp sites:
http://www.f-secure.com/download-purchase/updates.shtml
Manual Disinfection
To manually disinfect standalone malware (backdoors, worms, trojans, etc.) it is usually enough to delete all infected files from a computer and to restart it. Active malware files are usually locked by operating system so different disinfection approaches are required for different operating systems.
Please note that manual disinfection is a risky process, so it is recommended only for advanced users.
If Windows 95, 98 and ME operating system is used, it is recommended to restart a computer from a bootable system diskette and to delete an infected file from command prompt. For example, if a malicious file named ABC.EXE is located in Windows folder, it is usually enough to type the following command at command prompt:
DEL C:\WINDOWS\ABC.EXE
and to press Enter. After that an infected file will be gone. If Windows NT, 2000 or XP is used, a malicious file has to be renamed with a different extension (for example .VIR) and then a system has to be restarted. After restarting, the renamed malicious file will no longer be active and it can be easily to delete manually.
Malware Disinfection Tools
F-Secure provides disinfection tools for certain malware. These tools can be downloaded from this web page:
http://www.f-secure.com/download-purchase/tools.shtml
ftp://ftp.f-secure.com/anti-virus/tools/
Windows System Restore Issues
If Windows ME or XP is used, it is recommended to disable System Restore feature of these operating systems to prevent a computer from re-infection by an already removed malware. The fact is that System Restore feature of these operating systems might save an infected file into the special folder and copies it back to a hard drive it every time it has been renamed or deleted by F-Secure Anti-Virus or by a user. Instructions on how to disable System Restore feature are here:
Windows ME:
http://www.f-secure.com/v-descs/sfc_dis.shtml
Windows XP:
http://www.f-secure.com/v-descs/sfc_dis1.shtml
It is recommended to re-enable System Restore after disinfection in order to restore stable system configuration if any crash or incompatibility issue occurs in the future.
Failed Disinfection
In some cases, F-Secure Anti-Virus might not disinfect a system automatically. In this case, please visit our Support pages:
http://support.f-secure.com/enu/home/virusproblem/howtoclean/ |
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Detailed Description
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Trojan-Downloader:W32/Agent.BRK drops the following driver component once it has been executed:
- %sysdir%\drivers\runtime.sys
The component is detected as Rootkit.Win32.Agent.dw.
It also replaces the file for the Microsoft Windows IPv6 Windows Firewall Driver service:
- %sysdir%\drivers\ip6fw.sys
The file is replaced with a copy of Rootkit.Win32.Agent.dp.
The services are then installed and started.
Furthermore, Trojan-Downloader:W32/Agent.BRK launches an instance of Microsoft Internet Explorer as a hidden process with its code injected into the process.
It then attempts to connect to the following addresses:
- 66.246.72.173
- 67.18.114.98
- 208.66.194.241
The following address were seen from newer variants of this malware:
- 64.233.183.27
- 66.111.4.74
- 194.67.23.20
- 209.85.147.27
- 216.157.145.27
- 216.195.61.87
It attempts to download another malware component by sending an HTTP GET command with some details regarding the infected machine.
The downloaded file is then saved as:
- %sysdir%\[number]_exception.nls
The variable [number] is any number from 0 - 9.
The downloaded malware is currently detected as Rootkit.Win32.Agent.ey which makes the infected machine act as an e-mail spam bot.
Trojan-Downloader:W32/Agent.BRK may create any of the following mutex while active:
- k4j.32H_f7z_Z6e.g8G0
- y8w.61T_i0b_Q3f.l4R7
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F-Secure Corporation |
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Last Modified: January 29, 2008
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