Encyclopedia entry: TrojanDownloader:Win32/Renos.EK - Learn more about malware

TrojanDownloader:Win32/Renos.EK is a generic detection for a family of trojans that connect to certain websites in order to download arbitrary files. This may include other TrojanDownloader:Win32/Renos components, and rogue antivirus software such as Trojan:Win32/FakeSecSen or Trojan:Win32/FakeXPA.

System Changes

The following system changes may indicate the presence of this malware:

The presence of the following registry modifications (or similar):
Value: MSFox
With data: <full pathname of Win32/Renos.EK>
In subkey: HKCU\Software\Microsoft\Windows\CurrentVersion\Run

Value: Str<digit>
With data: <base64 encoded string> (for example, "x6tveq8ngbtmpknqirnnqauudxwx")
In subkey: HKLM\Software\Mozilla\MSFox

TrojanDownloader:Win32/Renos.EK is a generic detection for a family of trojans that connect to certain websites in order to download arbitrary files. This may include other TrojanDownloader:Win32/Renos components, and rogue antivirus software such as Trojan:Win32/FakeSecSen or Trojan:Win32/FakeXPA.

TrojanDownloader:Win32/Renos.EK may be distributed in the wild masquerading as a video codec. For an example, please see the image below:

Example method of distribution for Win32/Renos - masquerading as a video codec

It has also been observed being downloaded to affected machines after users are prompted by fake online security scanners. See below for examples of this method of distribution being utilized in the wild:

Example method of distribution for Win32/Renos - via fake online security scanners

Installation

When executed, TrojanDownloader:Win32/Renos.EK runs from its original location and modifies the registry to run the trojan downloader at each Windows start (for example):

Adds value: "MSFox" (or "Cognac")

With data: "<full pathname of Win32/Renos.EK>"

To subkey: HKCU\Software\Microsoft\Windows\CurrentVersion\Run

Additional registry modifications are made similar to the following example:

Adds value: Str<digit>

With data: <base64 encoded string> (for example, "x6tveq8ngbtmpknqirnnqauudxwx")

To subkey: HKLM\Software\Mozilla\MSFox

Note: These registry modifications may vary according to minor variant and the values listed may be different from those given in these examples.

Payload

Downloads and Executes Arbitrary Files

Once installed, the trojan may connect to one of a number of remote Web servers from which it may download and execute other files. In the wild, we have observed servers at the following locations being contacted in this manner by TrojanDownloader:Win32/Renos.EK:

image-big-library.com
22.250.166.222
167.156.220.15
erabl-pict.com

imagerepository.com

images-base.com

the-exefiles.com

freeexefiles.com

exefileformat.com

newexefile.com

Files downloaded may include other TrojanDownloader:Win32/Renos components, and rogue antivirus software such as Trojan:Win32/FakeSecSen or Trojan:Win32/FakeXPA. TrojanDownloader:Win32/Renos.EK has also been observed downloading files and other content associated with advertising and browser redirection.

TrojanDownloader:Win32/Renos may post system information to the remote server before downloading files. The downloaded malware is generally saved to the %temp% directory, using filenames such as "~tmpa.exe".

Analysis by Hamish O'Dea

Take the following steps to help prevent infection on your system:

Enable a firewall on your computer.
Get the latest computer updates for all your installed software.
Use up-to-date antivirus software.
Use caution when opening attachments and accepting file transfers.
Use caution when clicking on links to web pages.
Protect yourself against social engineering attacks.

Enable a firewall on your computer

Use a third-party firewall product or turn on the Microsoft Windows Internet Connection Firewall.

To turn on the Windows Firewall in Windows Vista

Click Start, and click Control Panel.
Click Security.
Click Turn Windows Firewall on or off.
Select On.
Click OK.

To turn on the Internet Connection Firewall in Windows XP

Click Start, and click Control Panel.
Click Network and Internet Connections. If you do not see Network and Internet Connections, click Switch to Category View.
Click Change Windows Firewall Settings.
Select On.
Click OK.

Get the latest computer updates

Updates help protect your computer from viruses, worms, and other threats as they are discovered. It is important to install updates for all the software that is installed in your computer. These are usually available from vendor websites.

You can use the Automatic Updates feature in Windows to automatically download future Microsoft security updates while your computer is on and connected to the Internet.

To turn on Automatic Updates in Windows Vista

Click Start, and click Control Panel.
Click System and Maintainance.
Click Windows Updates.
Select a setting. Microsoft recommends selecting Install updates automatically and choose a time that is convenient for you. If you do not choose Automatic, but you choose to be notified when updates are ready, a notification balloon appears when new downloads are available to install. Click the notification balloon to review and install the updates.

To turn on Automatic Updates in Windows XP

Click Start, and click Control Panel.
Click System.
Click Automatic Updates.
Select a setting. Microsoft recommends selecting Automatic. If you do not choose Automatic, but you choose to be notified when updates are ready, a notification balloon appears when new downloads are available to install. Click the notification balloon to review and install the updates.

Use up-to-date antivirus software

Most antivirus software can detect and prevent infection by known malicious software. To help protect you from infection, you should always run antivirus software that is updated with the latest signature files. Antivirus software is available from several sources. For more information, see http://www.microsoft.com/protect/computer/viruses/vista.mspx.

Use caution when opening attachments and accepting file transfers

Exercise caution with e-mail and attachments received from unknown sources, or received unexpectedly from known sources. Use extreme caution when accepting file transfers from known or unknown sources.

Use caution when clicking on links to web pages

Exercise caution with links to web pages that you receive from unknown sources, especially if the links are to a web page that you are not familiar with or are suspicious of. Malicious software may be installed in your system simply by visiting a web page with harmful content.

Avoid downloading pirated software

Threats may also be bundled with software and files that are available for download on various torrent sites. Downloading "cracked" or "pirated" software from these sites carries not only the risk of being infected with malware, but is also illegal. For more information. please see our article 'The risks of obtaining and using pirated software'.

Protect yourself from social engineering attacks

While attackers may attempt to exploit vulnerabilities in hardware or software in order to compromise a system, they also attempt to exploit vulnerabilities in human behavior in order to do the same. When an attacker attempts to take advantage of human behavior in order to persuade the affected user to perform an action of the attacker's choice, it is known as 'social engineering'. Essentially, social engineering is an attack against the human interface of the targeted system. For more information, please see our article 'What is social engineering?'.

Manual removal is not recommended for this threat. To detect and remove this threat and other malicious software that may have been installed, run a full-system scan with an up-to-date antivirus product such as the Microsoft online scanner (http://safety.live.com). For more information, see http://www.microsoft.com/protect/computer/viruses/vista.mspx.

TrojanDownloader:Win32/Renos.EK

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Summary

Symptoms