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Worm:W32/AutoRun.DMO

First posted on 12 December 2008.
Source: SecurityHome

Aliases :

There are no other names known for Worm:W32/AutoRun.DMO.

Explanation :

A standalone malicious program which uses computer or network resources to make complete copies of itself. May include code or other malware to damage both the system and the network.

right]This worm spreads through removable drives and network drives connected to an infected machine.

The payload of this worm is to infect all Microsoft Excel files on the infected machine, rendering the infected files unreadable. The data itself still remains and can be recovered, but the formatting and formulas used in the worksheet(s) may not always be recoverable.

Installation

During installation, the worm will create the following files:

• %Profiles%Default UserTemplates emp.tmp %Profiles%[UserName]Templates emp.tmp
• C:WINDOWSSystemcsrsss.exe
• C:WINDOWSSystemsvchosts.exe
• C:WINDOWSSystemwinxpsp2.dll

It will then modify the following files:

• %Profiles%Default UserTemplatesexcel.xls
  
• %Profiles%Default UserTemplatesexcel4.xls
• %Profiles%[UserName]excel.xls
  
• %Profiles%[UserName]excel4.xls

Next, the worm will search through all Excel files stored on the system and modify them. To do so, the worm drops a small temporary file (2KB in size) on every folder containing Excel files. The temporary file contains a bad string, " @ ", which is appended to every Excel file.



The actual search for Excel files is performed by two processes, svchosts.exe and csrsss.exe., which actively look for the targetted file types on the system. The constant searching results in the machine running a high CPU usage (usually 100%) for these processes. This high CPU usage is detectable by the user and is a sign of infection.


Propagation

The worm itself, and its autorun file, propagates through any accessible removable drive and every root folder.

The autorun for this worm appears as:

• [autorun]
  Shellexecute=data.exe
  shellopen=&Open...
  shellopenCommand=data.exe
  shellexplore=&Explorer
  shellexploreCommand="data.exe -e"

Registry

During installation, the worm registers itself so that it will run automatically on every system startup.

• [HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun]
  Microsoft OfficeTool = "svchosts.exe"

Recovery

The infected files can be partially recovered by using Microsoft Excel's built-in repair function. Manual recovery is needed to fully recover all elements of an infected file, and involves stripping off the bad string and replacing the Excel header. Please note that this works on some, but not all, infected files.

Last update 12 December 2008

 

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