A worm that spreads via e-mail, usually in infected executable e-mail file attachments.
Depending on the settings of your F-Secure security product, it will either automatically delete, quarantine or rename the suspect file, or ask you for a desired action.
More information on the scanning and removal options available in your F-Secure product can be found in the Help Center.
You may also refer to the Knowledge Base on the F-Secure Community site for more information.
Email-Worm:W32/Sober.F is written in Visual Basic. The worm's file is a PE executable of length 42496 bytes, packed with a modified version of UPX file compressor. The worm has its own SMTP engine that it uses to send out infected e-mail messages.
When the worm's file is run, it opens Notepad with a text file as a disguise:
Then the worm installs itself to system. It copies itself to Windows System folder once, with a semi-randomly generated name and creates 2 startup keys for this file in System Registry. The worm uses the following fixed text strings to generate the name of its file and the name of the startup key:
The worm also creates 3 empty files in the same folder:
These files disable previous Sober variants if they are installed on an affected computer.
The worm creates a startup Registry key to its semi-randomly named file in System Registry:
The subkey name that is created by the worm is semi-randomly generated too. The value of a subkey is the path the worm's file in Windows System folder.
Sober.F worm constantly checks a hard drive for the presence of the file named CVQAIKXT.APK. If this file is found, the worm unloads itself from memory. Also if this file is present on a hard disk during the worm's installation process, the worm does not copy itself to a hard drive.
Sober.F denies access to its data and executable files if it is active in Windows memory.
The worm scans files with certain extensions on all hard disks to harvest e-mail addresses. Files with the following extensions are scanned:
The worm can send messages chosen from variety of templates in English and German. Some of the messages will attempt tp appear to the eyes of the users as harmless error messages. Possible text appearing in those messages is:
220.127.116.11_failed_after_I_sent_the_message./Remote_host_said: _554_delivery_error:_dd_Sorry_your_message_cannot_be_delivered ._This_account_has_been_disabled_or_discontinued_[#102]._-_ mta134.mail. dcn.com ** End of Transmission The original message is a separate attachment. --- Mail To: UserHelp Error_Info _attach Read the attachment for details. Bad Gateway: The message has been attached. +++ A service of +++ Mail: home -attachment The message has been attached. attach-message Database #Error -- Partial message is available! -- Error: llegal signs in Mail-Routing -- Mail Server: ESMTP VX32.9 Version Betha Alpha
It also composes messages in such a way that they look as if scanned by some Anti-Virus and found clean. Messages will resemble:
++++ Im www erreichbar unter: http://www.[url chosen by the worm] ++++ E-Mail: [email chosen by the worm] *** Anti- Virus: Es wurde kein Virus erkannt *** [name chosen by the worm] Virenschutz *** http://www.[url chosen by the worm]
The text can be preceded by some other german sentence, and some of the strings may also differ from message to message.
Detection of Sober.F is available in the following FSAV updates:
Detection Type: PC