F-Secure Virus Descriptions : Sircam

 [HKCR\exefile\shell\open\command]

is changed to '""[windows_drive]\recycled\SirC32.exe" "%1" %*"'. This is done to activate a worm's copy every time an EXE file is started. Since the recycled folder name is hardcoded the worm does not work on machines with NTFS filesystem. Most Windows NT and 2000 systems are installed on NTFS.

2. The worm copies itself as 'SCam32.exe' in the System directory. The worm then creates a startup key for this file in the Registry to be started during all Windows sessions:

 [HKLM\Software\Microsoft\Windows\CurrentVersion\RunServices]
 "Driver32" = "<windows_system_dir_name>\SCam32.exe"

3. The worm copies itself as 'rundll32.exe' file to Windows directory. The original 'rundll32.exe' file is renamed to 'run32.exe'. This copy exists only if a computer got infected through a network share (see below).

4. Sometimes (once out of 33 cases) the worm places its copy to Windows directory with the 'ScMx32.exe' name. In this case another copy of the worm is created in the current user's personal startup folder as 'Microsoft Internet Office.exe'. This copy will be started when a user who got infected logs into a system.

When a Sircam-infected e-mail attachment is opened it shows the document it picked up from the sender machine's. The file is displayed with the appropiate program according to it's extension:

 '.DOC': WinWord.exe or WordPad.exe
 '.XLS': Excel.exe
 '.ZIP': winzip.exe

This effectively disguises the worm's activity. While the user is checking the document the system get infected (as described above).

The worm uses Windows Address Book to collect e-mail addresses ('*.wab files). The worm also tries to look for e-mail addresses in \Temporary Internet Files\ folder ('sho*', 'get*', 'hot*', '*.html'). If a user has a working e-mail account the worm reads the its setting. Otherwise the '[username]@prodigy.mx.net' is used as the default sender's address and 'prodigy.net.mx' is used for the SMTP server name. The worm has its own SMTP engine and it sends out messages using this engine.

The worm collects a list of files with certain extensions ('.DOC', '.XLS', '.ZIP') into fake DLL files named 'sc*.dll'. The worm then sends itself out with one of the document files it found in a users's 'My Documents' folder.

Messages sent by Sircam look like this:

 From: [user@address]
 To: [user@address]
 Subject: [document name without extension]

 Hi! How are you?

 'I send you this file in order to have your advice'

 'I hope you can help me with this file that I send'

 'I hope you like the file that I sendo you'

 'This is the file with the information that you ask for'

 See you later. Thanks

If a system's language is set to Spanish the worm sends messages in Spanish:

 Hola como estas ?

 'Te mando este archivo para que me des tu punto de vista'

 'Espero me puedas ayudar con el archivo que te mando'

 'Espero te guste este archivo que te mando'

 'Este es el archivo con la informaci n que me pediste'

 Nos vemos pronto, gracias.

The attached file has the name of a picked document file with a double extension like '.DOC.EXE', '.XLS.PIF'. The '.COM', '.BAT', '.PIF' and '.LNK' are used as second (executable) extensions. Since the worm can pick any of the user's personal document it migh send out confidential information.

This worm also uses Windows network shares to spread. When doing this, it first enumerates all the network shares available to the infected computer. If there there is a writeable \recycled\ folder on a share, a copy of the worm is put to \\[share]\recycled\' folder as 'SirCam32.exe' file. The \\[share]\autexec.bat file is appended with an extra line: '@win \recycled\SirC32.exe', so next time when an infected computer is rebooted the worm will be started. The worm also copies itself as 'rundll32.exe' file to Windows directory of a remote system. The original 'rundll32.exe' file is copied to 'run32.exe' before that.

Payloads

The worm has two payloads. On 16th of October in one case out of 20 it deletes everything from the drive where Windows is installed. On any other day in one of 50 cases it fills up the drive where Windows is installed. In this case it creates a file called '<windows drive>:\recycled\sircam.sys' and continuously fills it with one of below given text strings until the hard drive space is consumed.

 '[SirCam_2rP_Ein_NoC_Rma_CuiTzeO_MicH_MeX]'

or

 '[SirCam Version 1.0 Copyright  2001 2rP  Made in / Hecho en
  - Cuitzeo, Michoacan Mexico]'

Fortunately none of these payloads work due to bugs in the trigger routine. The random number generator in not initialized in the beginning so the worm will not activate it's payloads on 16th of October or on any other day.

Removal instructions:

If your system is infected with the worm first please download this REG file and install it (by double-clicking on it):

ftp://ftp.europe.f-secure.com/anti-virus/tools/sirc_dis.reg

This will remove the worm's reference from the EXE file startup key and the main worm's startup key in the Registry.

Warning! The system might become unusable if the worm's file is deleted without modifying the EXE file startup key first.

After that the system can be safely disinfected with F-Secure Anti-Virus. If for some reason the worm's file can't be deleted from Windows (locked file), then you have to exit to pure DOS and delete the worm's file manually or use a DOS-based scanner (F-Prot for DOS for example). Note that for 100% disinfection all worm's files needs to be deleted and Registry should be fixed (see above).

Additional Note: If a workstation was infected trough a network share '\windows\run32.exe' has to be renamed back to '\windows\rundll32.exe' after disinfection.

The extra line in 'autoexec.bat' file that starts the worm from \recycled\ folder should be removed also.

Network infection prevention:

If a network is infected and it is not possible to take it down to disinfect all workstations, the following method can prevent the worm from spreading to clean workstations:

In the \Recycled\ folder of a drive where Windows is installed, it is needed to create a dummy file with SIRC32.EXE name and read-only attribute.

[Analysis: Gergely Erdelyi, Alexey Podrezov; F-Secure Corp.; July 18-23, 2001]