Analysis by: Christopher Daniel So
ALIASES:

TrojanDownloader:Win32/Unruy.H (Microsoft), Trojan.Gen (Symantec), Downloader.a!us (McAfee), Trojan.Win32.Inject.blwr (Kaspersky)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

 OVERALL RISK RATING:
 DAMAGE POTENTIAL:
 DISTRIBUTION POTENTIAL:
 REPORTED INFECTION:

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

This Trojan arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

It uses the Windows Task Scheduler to add a scheduled task that executes the copies it drops.

  TECHNICAL DETAILS

File Size: 38,400 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 26 Oct 2011

Arrival Details

This Trojan arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

Installation

This Trojan drops the following copies of itself into the affected system:

  • %System%\Yic8dpB.com

It uses the Windows Task Scheduler to add a scheduled task that executes the copies it drops.

Autostart Technique

The scheduled task executes the malware at the following period:

  • everyday at 12:54 AM, 1:54 AM, 2:54 AM, 3:54 AM, 4:54 AM, 5:54 AM, 6:54 AM, 7:54 AM, 8:54 AM, 9:54 AM, 10:54 AM, 11:54 AM, 12:54 PM, 1:54 PM, 2:54 PM, 3:54 PM, 4:54 PM, 5:54 PM, 6:54 PM, 7:54 PM, 8:54 PM, 9:54 PM, 10:54 PM and 11:54 PM

Other System Modifications

This Trojan adds the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Schedule
AtMaxHours = "48"

  SOLUTION

Minimum Scan Engine: 9.200

Step 1

For Windows XP and Windows Server 2003 users, before doing any scans, please make sure you disable System Restore to allow full scanning of your computer.

Step 2

Restart in Safe Mode

[ Learn More ]

Step 3

Delete this registry value

[ Learn More ]

Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this step only if you know how or you can ask assistance from your system administrator. Else, check this Microsoft article first before modifying your computer's registry.

  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Schedule
    • AtMaxHours = "48"

Step 4

To delete the added job file:

  1. Click on Start>Programs>Accessories>System Tools>Scheduled Tasks
  2. Double-click on a job file.
  3. Check if the malware path and file name is in the Run: box.
  4. If it does, delete the job file.
  5. Repeat step 2-4 for the remaining job files.

Step 5

Restart in normal mode and scan your computer with your Trend Micro product for files detected as TROJ_UNRUY.ZP. 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.


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