Name :	Email-Worm:W32/Sober.AA
Category:	Malware
Type:	Email-Worm
Platform:	W32
Date of Discovery:	April 07, 2007

Sober.AA is a mass mailing worm that uses English and German texts in the e-mails generated by this worm.

Automatic Disinfection

Usually standalone malware (backdoors, worms, trojans, etc.) is automatically removed by F-Secure Anti-Virus (FSAV) starting from version 5.40. Malware files get automatically renamed by FSAV, so they can not be started any more. In some rare cases, when automatic disinfection is not possible, a user can select disinfection action by him/herself to make FSAV rename or delete an infected file. In some special cases it is recommended to use specific disinfection tools provided by F-Secure. They can be downloaded from our ftp site:

ftp://ftp.f-secure.com/anti-virus/tools/

F-Secure Anti-Virus can be purchased from our webshop or from our authorised distributors. A trial version F-Secure Anti-Virus, limited to 30 days, can be downloaded from our website:

http://www.f-secure.com/download-purchase/

All the latest versions of FSAV can download anti-virus database updates automatically. However, these updates can be also downloaded and installed manually from our web or ftp sites:

http://www.f-secure.com/download-purchase/updates.shtml


Manual Disinfection

To manually disinfect standalone malware (backdoors, worms, trojans, etc.) it's usually enough to delete all infected files from a computer and to restart it. Active malware files are usually locked by operating system so different disinfection approaches are required for different operating systems.
Please note that manual disinfection is a risky process, so it is recommended only for advanced users.

If Windows 95, 98 and ME operating system is used, it is recommended to restart a computer from a bootable system diskette and to delete an infected file from command prompt. For example if a malicious file named ABC.EXE is located in Windows folder, it is usually enough to type the following command at command prompt:

DEL C:\WINDOWS\ABC.EXE

and to press Enter. After that an infected file will be gone. If Windows NT, 2000 or XP is used, a malicious file has to be renamed with a different extension (for example .VIR) and then a system has to be restarted. After restart a renamed malicious file will no longer be active and it can be easily deleted manually.


Malware Disinfection Tools

F-Secure provides disinfection tools for certain malware. These tools can be downloaded from this webpage:

http://www.f-secure.com/download-purchase/tools.shtml

ftp://ftp.f-secure.com/anti-virus/tools/


Windows System Restore Issues

If Windows ME or XP is used, it is recommended to disable System Restore feature of these operating systems to prevent a computer from re-infection by an already removed malware. The fact is that System Restore feature of these operating systems might save an infected file into the special folder and copy it back to a hard drive it every time it's been renamed or deleted by F-Secure Anti-Virus or by a user. Instructions on how to disable System Restore feature are here:

Windows ME:
http://www.f-secure.com/v-descs/sfc_dis.shtml

Windows XP:
http://www.f-secure.com/v-descs/sfc_dis1.shtml

It is recommended to re-enable System Restore after disinfection in order to restore stable system configuration in the future, if any crash or incompatibility issue occurs.


Failed Disinfection

In some cases F-Secure Anti-Virus might not disinfect a system automatically. In this case please visit our Support pages:

http://support.f-secure.com/enu/home/virusproblem/howtoclean/

This worm is written in Visual Basic. It is compressed using UPX.

Installation to the System

Upon execution, this worm creates the folder PoolData in the Windows directory. It then creates several copies of itself as follows:


These files are identical to each other with a single byte difference located at offset 0xA0.

This worm also creates the following Registry entries in order to enable its automatic execution upon system start up:


Spreading via E-mail messages

Before spreading, this worm scans files with certain extensions on all hard disk drives to harvest e-mail addresses. All files with the following extensions are scanned:


This worm creates the following files, where the system harvested e-mail addresses are stored:


It can then send e-mails with English and German based text together with a Zip archived copy of itself as an attachment.

It ignores any email addresses that contain any of the following substrings:


The worm composes the following German messages:

Subject:


Body:


Attachment:


--- or ---

Subject:


Body:

Attachment:


--- or ---

Subject:


Body:


Attachment:


It also composes the following English messages:

Subject:


Body:


Attachment:


--- or ---

Subject:


Body:


Attachment:


These e-mail messages may appear to come from the following senders: