TrojanDownloader:Win32/Renos.OJ 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.OJ may be distributed in the wild masquerading as a video codec. For an example, please see the image below:
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:
Installation
When executed, TrojanDownloader:Win32/Renos.OJ runs from its original location and modifies the registry to run the trojan downloader at each Windows start (for example):
In subkey: HKCU\Software\Microsoft\Windows\CurrentVersion\Run
Sets value: "MSFox" (or "Cognac")
With data: "<full pathname of Win32/Renos.OJ>"
Additional registry modifications are made similar to the following example:
In subkey: HKLM\Software\Mozilla\MSFox
Sets value: Str<digit>
With data: <base64 encoded string> (for example, "x6tveq8ngbtmpknqirnnqauudxwx")
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.OJ:
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.OJ 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 computer:
Enable a firewall on your computer.
Get the latest computer updates for all your installed software.
Use up-to-date antivirus software.
Limit user privileges on the computer.
Use caution when opening attachments and accepting file transfers.
Use caution when clicking on links to webpages.
Avoid downloading pirated software.
Protect yourself against social engineering attacks.
Use strong passwords.
Enable a firewall on your computer
Use a third-party firewall product or turn on the Microsoft Windows Internet Connection Firewall.
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.
Use up-to-date antivirus software
Limit user privileges on the computer
Starting with Windows Vista and Windows 7, Microsoft introduced User Account Control (UAC), which, when enabled, allowed users to run with least user privileges. This scenario limits the possibility of attacks by malware and other threats that require administrative privileges to run.
You can configure UAC in your computer to meet your preferences:
Use caution when opening attachments and accepting file transfers
Exercise caution with email 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 webpages
Exercise caution with links to webpages that you receive from unknown sources, especially if the links are to a webpage that you are not familiar with, unsure of the destination of, or suspicious of. Malicious software may be installed in your computer simply by visiting a webpage 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, see '
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 to compromise a computer, they also attempt to exploit vulnerabilities in human behavior to do the same. When an attacker attempts to take advantage of human behavior 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 computer. For more information, see '
What is social engineering?'.
Use strong passwords
Attackers may try to gain access to your Windows account by guessing your password. It is therefore important that you use a strong password – one that cannot be easily guessed by an attacker. A strong password is one that has at least eight characters, and combines letters, numbers, and symbols. For more information, see
http://www.microsoft.com/protect/yourself/password/create.mspx.
