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Also Called: Trojan.AndroidOS.Koler.a.
Virus Type: Ransomware (mobile)

What is it?

Koler is a hidden part of the malicious campaign which has introduced Koler 'police' mobile ransomware for Android devices to the world in April 2014. This part includes some browser-based ransomware and an exploit kit.

Those behind the attacks employed an unusual scheme to scan victims’ systems and offer customized ransomware depending on location and device type – mobile or PC. The redirection infrastructure is the next step, after a victim visits any of at least 48 malicious porno websites used by Koler’s operators. The use of a pornographic network for this ransomware is no coincidence: victims are more likely to feel guilty about browsing such content and pay the alleged fine from the ‘authorities’.

Since July 23 the mobile component of the campaign has been disrupted, as the command and control server started sending ‘Uninstall’ commands to mobile victims, effectively deleting the malicious application. However, the rest of the malicious components for PC users – including the exploit kit – are still active.

Virus Details

48 porno sites redirect users to the central hub that uses the Keitaro Traffic Distribution System (TDS) to redirect users again. Depending on a number of conditions, this second redirection can lead to three different malicious scenarios:

- Installation of the Koler mobile ransomware. In case of mobile engagement the website automatically redirects the user to the malicious application. But the user still has to confirm the download and installation of the app – called animalporn.apk – which is actually Koler ransomware. It blocks the screen of an infected device and requests a ransom of between $100 and $300 in order to unlock it. The malware displays a localized message from the 'police', making it more realistic.

- Redirection to any of the browser ransomware websites. A special controller checks whether (i) the user agent is from one of 30 affected countries, (ii) the user isn’t an Android user, and (iii) the request contains no Internet Explorer user agent. If it’s yes to all three, the user sees a blocking screen identical to the one used for mobile devices. There is no infection in this case, just a pop-up showing a blocking template. However, the user can easily avoid the block with a simple alt+F4 combination.

- Redirection to a website containing the Angler Exploit Kit. If the user uses Internet Explorer, then the redirection infrastructure used in this campaign sends the user to sites hosting the Angler Exploit Kit, which has exploits for Silverlight, Adobe Flash and Java. During Kaspersky Lab’s analysis, the exploit code was fully functional; however, it didn’t deliver any payload, but this may change in the nearest future.

Recommendations for staying safe

  • Remember that you will never get official 'ransom' messages from the police, so never pay them;
  • Don’t install any app you find while browsing;
  • Don’t visit websites you don’t trust;
  • Use a reliable antivirus solution.

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Koler 'police' mobile ransomware

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