Worm:VBS/HeadTail.A

UPDATE (July 22 2009):

F-Secure Anti-Virus products had a brief False Alarm with this detection. A clean file called avh_fsav_800_bin was detected as being infected on 21 July 2009. This has now been fixed with the database update, 2009-07-21_10.If the avh_fsav_800_bin file was removed, it will be recreated automatically and there is no need for further action by the user. We apologize for any inconvenience.

Technical Description

Worm:VBS/HeadTail.A is a Visual Basic Script worm that propagates by copying itself to available removable, fixed, and remote drives. It is also able to delete predefined files and processes.

Execution

Whenever the specified drive is accessed in systems with Drive Type Autorun Enabled settings, the malware will automatically execute itself.Upon execution, this malware will search in removable, fixed, and remote drives for HTA, HTM, HTML, ASP and VBS files whose file size is less than 350000 Bytes to infect. It then creates a autorun registry entry in :

• HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Windows\Load

As a way to infect more files and enable additional executions, the worm modifies the file association of the following file types to execute the malware first:

• .CHM
• .HLP
• .REG
• .TXT

As part of the malware's restrictions in terms of infection, the malware will infect no more than 1000 files that is found on single execution.HeadTail.A uses the System and Hidden file properties and sets the registry to disable viewing of files with such attributes in order to hide from the user.

Payload

HeadTail.A checks the filename and if it contains predefined strings (supposedly related to adult videos), it will delete the file. The file formats are as below:

• .AVI
• .MPG
• .RM
• .RMVB

It will also monitor and ensure that the following processes are terminated :

• 360tray.exe
• cmd.com
• cmd.exe
• msconfig.exe
• ras.exe
• regedit.com
• regedit.exe
• regedit.pif
• regedit.scr
• SREng.exe
• taskmgr.exe
• USBAntiVir.exe

Based on the parameters, HeadTail.A is capable of removing all system modifications and deleting all its copies. It can also disinfect all infected files accessible in the system.