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Added to the Dr.Web virus database: 2013-04-05

Virus description added:

A malicious program designed to inject arbitrary content into webpages loaded in browser windows.

Once launched, it determines the infected computer ID based on the data on equipment, computer name, and current user name.

Then it copies its executable file into

C:\Users\<username>\My Documents\MyApplicationData\~backup.exe

and modifies the system registry as follows:

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run] "~backup~"="C:\Users\<username>\My Documents\MyApplicationData\~backup.exe" specifying the path to the dropper to be deleted as follows: "~tempbackup~"="<path to the dropper>"

On 32-bit systems

The Trojan launches a copy of explorer.exe and gets injected into this copy. Then it reads its own file and deletes the dropper if the file's name does not contain the “~backup” string. Injections are accompanied by modification of the following file:

C:\Users\<username>\My Documents\MyApplicationData\~backup.dat

On 64-bit systems

The Trojan modifies the system registry branch that manages the autorun list, runs its executable file and its own copy, and deletes the dropper's file. The malicious program verifies the presence of its two copies in the infected computer's memory and of the corresponding entries in the system registry.

Then it scans the system for installed anti-virus programs by looking through the names of active processes.

MsMpEng.exe, msseces.exe, avp.exe, dwengine.exe, dwservice.exe, ecls.exe, egui.exe, ekrn.exe, AvastUI.exe, AvastSvc.exe, avgnt.exe, avguard.exe, avshadow.exe, avgnsx.exe, avgrsx.exe, avgtray.exe, ccsvchst.exe, vba32ldr.exe, vbaScheduler.exe, Mcshield.exe, Mctray.exe, bdagent.exe, coreServiceShell.exe, uiSeAgnt.exe

By checking the names of the following processes, the Trojan attempts to determine whether it is running in a virtual environment or not:


Once installed, Trojan.Mayachok.18607 tries to inject itself into all Windows processes, including processes of launched browsers.

The configuration file is saved into c:\Users\<username>\Cookies\cf. Then the Trojan sends requests to a number of addresses and gets a new configuration file, which may contain a command to download an executable file. The executable file is saved into the following folder:

C:\Users\<username>\My Documents\MyApplicationData\~dwnld.exe

After that, the file is run.

Moreover, the configuration file contains a script injected by the Trojan into all webpages browsed by the user.

Curing recommendations

  1. If the operating system (OS) can be loaded (either normally or in safe mode), download Dr.Web Security Space and run a full scan of your computer and removable media you use. More about Dr.Web Security Space.
  2. If you cannot boot the OS, change the BIOS settings to boot your system from a CD or USB drive. Download the image of the emergency system repair disk Dr.Web® LiveDisk , mount it on a USB drive or burn it to a CD/DVD. After booting up with this media, run a full scan and cure all the detected threats.
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Use Dr.Web Anti-virus for macOS to run a full scan of your Mac.

After booting up, run a full scan of all disk partitions with Dr.Web Anti-virus for Linux.

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  1. If the mobile device is operating normally, download and install Dr.Web for Android. Run a full system scan and follow recommendations to neutralize the detected threats.
  2. If the mobile device has been locked by Android.Locker ransomware (the message on the screen tells you that you have broken some law or demands a set ransom amount; or you will see some other announcement that prevents you from using the handheld normally), do the following:
    • Load your smartphone or tablet in the safe mode (depending on the operating system version and specifications of the particular mobile device involved, this procedure can be performed in various ways; seek clarification from the user guide that was shipped with the device, or contact its manufacturer);
    • Once you have activated safe mode, install the Dr.Web for Android onto the infected handheld and run a full scan of the system; follow the steps recommended for neutralizing the threats that have been detected;
    • Switch off your device and turn it on as normal.

Find out more about Dr.Web for Android