Analysis by: Rhena Inocencio


Ransom:Win32/LockScreen.AO (Microsoft), Trojan.Win32.Waldek.ism (Kaspersky)




  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes


Infection Channel:

Downloaded from the Internet

This malware is seen being distributed by the Magnitude Exploit Kit. It exploits a vulnerability in the Windows kernel (CVE-2015-1701) to download a LOCKY ransomware.

To get a one-glance comprehensive view of the behavior of this Trojan, refer to the Threat Diagram shown below.

This Trojan executes the downloaded files. As a result, malicious routines of the downloaded files are exhibited on the affected system.

It takes advantage of certain vulnerabilities.


File Size:

36,352 bytes

File Type:


Memory Resident:


Initial Samples Received Date:

13 Apr 2016


Connects to URLs/IPs, Downloads files

Arrival Details

This malware arrives via the following means:

  • distributed by exploit kit

Download Routine

This Trojan accesses the following websites to download files:

  • http://{BLOCKED}

It saves the files it downloads using the following names:

  • %Temporary Internet Files%\Content.{browser}\{random folder name}\bg[number].gif

(Note: %Temporary Internet Files% is the Temporary Internet Files folder, where it usually is C:\Documents and Settings\{user name}\Local Settings\Temporary Internet Files on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local\Microsoft\Windows\Temporary Internet Files on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), and Windows Server 2008; C:\Users\{user name}\AppData\Local\Microsoft\Windows\INetCache on Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), and Windows Server 2012.)

Trend Micro detects the dowloaded file as:

  • Ransom_LOCKY.PUY

It then executes the downloaded files. As a result, malicious routines of the downloaded files are exhibited on the affected system.

Other Details

This Trojan takes advantage of the following vulnerabilities:


Minimum Scan Engine:


Step 1

Before doing any scans, Windows XP, Windows Vista, and Windows 7 users must disable System Restore to allow full scanning of their computers.

Step 2

Note that not all files, folders, and registry keys and entries are installed on your computer during this malware's/spyware's/grayware's execution. This may be due to incomplete installation or other operating system conditions. If you do not find the same files/folders/registry information, please proceed to the next step.

Step 3

Scan your computer with your Trend Micro product and note files detected as TROJ_LOCKY.DLDRA

Step 4

Remove the malware/grayware file dropped/downloaded by TROJ_LOCKY.DLDRA. (Note: Please skip this step if the threat(s) listed below have already been removed.)

    • Ransom_LOCKY.PUY

Step 5

Restart in Safe Mode

[ Learn More ]

Step 6

Search and delete the file detected as TROJ_LOCKY.DLDRA

[ Learn More ]
Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden files in the search result.

Step 7

Restart in normal mode and scan your computer with your Trend Micro product for files detected as TROJ_LOCKY.DLDRA. If the detected files have already been cleaned, deleted, or quarantined by your Trend Micro product, no further step is required. You may opt to simply delete the quarantined files. Please check this Knowledge Base page for more information.

Step 8

Download and apply this security patch Refrain from using these products until the appropriate patches have been installed. Trend Micro advises users to download critical patches upon release by vendors.

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