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The current case “DNSChanger” – what computer users can do now

19
Jan
2012

There are two different characteristics of “DNSChanger” malware which should become clear with the following explanation:

Character 1:
The malware modifies the DNS settings on an infected Windows PC. These settings include the “hosts” file and the DHCP settings.
If the DNS settings are changed, a user does not reach the website he/she intended to reach when using the web browser. The attacker redirects the user to a predefined target.

Character 2:
The malware modifies the name server settings within the router.
This means, that the changes are not directly made on a PC but on the router, which, e.g. connects the home network with the Internet. 
The Trojan is equipped with password lists which contain the standard log ins for the most common routers on the market. The Trojan can easily gain access to the router’s web interface in case the user never edited the standard factory-set password. This way, the bad guys can change telecommunication service provider’s name server settings for their individual purposes and control each and every user attempt to open a website.

What is going to happen on 8 March 2012?
The FBI will shut down the formerly rogue DNS servers they now have under their control. This means that all users with computers which 

  • are infected with the “DNSChanger” malware spread by the bad guys and
  • have not set their DNS settings to “normal” state

can expect to experience problems connecting to the WWW after the FBI took down the DNS servers.

 

How can I test my Internet settings?
At this point, we present measures computer users with Microsoft Windows operating systems (XP, Vista and 7) can perform themselves to check their PC for immediate damages caused by “DNSChanger” malware.
If the device to be tested is a computer in a company’s network, please contact your system administrator first. 

Before you manually start testing the settings described below, perform a complete antivirus scan on your entire PC. After that, visit the website dns-ok.de
If this website shows a red warning sign (see below), you inevitably have to go through the steps described below. 
If the website displays a green bar, the DNS settings of your system and router are ok and there has been no manipulation by the current “DNSChanger” malware. Please be aware that this online test can only be performed flawlessly without any proxy settings in the browser.

Picture of warning message on dns-ok.de

Attention: If the online test or the manual tests presented show your DNS settings are correct, this does not necessarily mean your computer is free from malware! In any case, please conduct regular computer scans with comprehensive and up-to-date antivirus software, e.g. G Data InternetSecurity 2012 with BootCD.

 

On the PC
Step 1: Check the “hosts” file
Open a text editor. When using Windows Vista or Windows 7, run the text editor as administrator. To do so, right-click the text editor executable file and then left-click “Run as administrator”.

Now, within this text editor, open the “hosts” file. You can find it under
C:\Windows\system32\drivers\etc
You might have to choose “All files (*.*)” at the bottom right corner of the file selector window to see and subsequently select the “hosts” file.

When using Windows XP, the “hosts” file contains only one entry: localhost is connected to 127.0.0.1
The default “hosts” file under Microsoft Windows Vista and Microsoft Windows 7 contains no entry at all. Note: All lines starting with a hash (#) character are comment lines and are therefore ignored by the system and can be ignored by you as well.

Picture of a

If you see additional entries in your “hosts” file, without a preceding hash character and regardless of the operating system, this can be an indication of a modification made by malware.

You can add a hash character to the beginning of each line with an additional entry to verify the situation. Restart your browser if necessary and visit the website dns-ok.de

Step 2: Check the DHCP settings
Users with a Windows XP computer need to click Start > Control panel > Network and Internet Connections > Network Connections and choose the active connection they are using to access the Internet. Right-click the connection and choose “Properties”.
Windows Vista and Windows 7 users click Start > Control panel > Network and Sharing Center and choose the active connection you are using to access the Internet as well, click and choose “Properties”.

The option “Properties” will open up a new window (see screenshot 3).
Choose Internet Protocol (TCP/IP) under Windows XP and Internet Protocol Version 4 (TCP/IPv4) under Windows Vista and Windows 7. In any case, the options “Obtain an IP address automatically” and “Obtain DNS server address automatically” should be activated. If you can find any unknown DNS server address at this point, delete the IP and activate “Obtain DNS server address automatically”.

Following this, open the Windows command-line shell (Start > All Programs > Accessories > Command Prompt). Windows Vista users have to run this command prompt as administrator to make the following instruction work. In the command prompt, type ipconfig /flushdns and execute it by pressing the enter key. This short command empties the system’s DNS cache. Restart your browser if necessary and visit the website dns-ok.de

Step 3: Check the browser settings
Microsoft Internet Explorer (Version 9)
Click “Tools” > “Internet options”. Then choose “Connections”. Click “LAN settings” and check whether one of the three possible boxes is ticked. None of them should be ticked by default.

Mozilla Firefox (Version 9)
Click “Tools” > “Options” > and choose the “Advanced” tab. Then, choose the “Network” tab and “Settings” in the “Connection” section. Now check whether you see any entry in “Manual Proxy settings”. By default, “No Proxy” should be activated.

Google Chrome (Version 16)
Click “Customize and control Google Chrome” and choose “Options” and then “Under the Hood”. In the “Network” section, click “Change proxy settings”. As Google Chrome uses the computer system’s proxy settings, the Google Chrome settings are equivalent to the ones the Internet Explorer has.
Picture of the sytsem's proxy settings, available in IE and Google Chrome
In the newly opened window, click “LAN settings” and check whether one of the three possible boxes is ticked. None of them should be ticked by default.

After checking your browser settings, restart the browser if necessary and visit the website dns-ok.de

On the router
Step 4: Check the router’s network settings
If several computers in one local network are experiencing the potential “DNSChanger” problems, access your router via web interface. Please refer to the manual of your specific device to see how this access works.

By default, the setting “Obtain an IP address automatically” should be activated. If you can see DNS server addresses at this point, delete those. Restart your router.
Subsequently, open the Windows command-line shell (Start > All Programs > Accessories > Command Prompt) on any PC of the local network. Windows Vista users have to run this command prompt as administrator to make the following instruction work. In the command prompt, type ipconfig /flushdns and execute it by pressing the enter key. This short command empties the system’s DNS cache. Restart your browser if necessary and visit the website dns-ok.de

For security reasons, you should furthermore change your router password immediately. This password change is especially important if you have never changed the factory-set password and also in case you now found settings on your router, which have been made by any unauthorized third party. 

Attention: If the online test or the manual tests presented show your DNS settings are correct, this does not necessarily mean your computer is free from malware! In any case, please conduct regular computer scans with comprehensive and up-to-date antivirus software, e.g. G Data InternetSecurity 2012 with BootCD.
 

You can download the information given in this blog post as a PDF:
G Data SecurityLabs "DNSChanger" Information (English)
G Data SecurityLabs "DNSChanger" Informtaion (German)

General advice

  • Use an up-to-date, comprehensive security solution with a virus scanner, firewall, spam filter, http scan and real-time protection. A spam filter, to get rid of unwanted spam, is a must-have, too.
  • Always keep your software, browser and operating system up-to-date and regularly install updates to close existing security vulnerabilities.
  • Change the factory-set passwords on devices right after configuring those devices.
  • If you realize your computer has been infected, change all passwords in use, e.g. for (online) email accounts, online-banking accounts, shopping websites, social networks, instant messengers and many more.

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