Parent class: VirWare

Viruses and worms are malicious programs that self-replicate on computers or via computer networks without the user being aware; each subsequent copy of such malicious programs is also able to self-replicate. Malicious programs which spread via networks or infect remote machines when commanded to do so by the “owner” (e.g. Backdoors) or programs that create multiple copies that are unable to self-replicate are not part of the Viruses and Worms subclass. The main characteristic used to determine whether or not a program is classified as a separate behaviour within the Viruses and Worms subclass is how the program propagates (i.e. how the malicious program spreads copies of itself via local or network resources.) Most known worms are spread as files sent as email attachments, via a link to a web or FTP resource, via a link sent in an ICQ or IRC message, via P2P file sharing networks etc. Some worms spread as network packets; these directly penetrate the computer memory, and the worm code is then activated. Worms use the following techniques to penetrate remote computers and launch copies of themselves: social engineering (for example, an email message suggesting the user opens an attached file), exploiting network configuration errors (such as copying to a fully accessible disk), and exploiting loopholes in operating system and application security. Viruses can be divided in accordance with the method used to infect a computer:
  • file viruses
  • boot sector viruses
  • macro viruses
  • script viruses
Any program within this subclass can have additional Trojan functions. It should also be noted that many worms use more than one method in order to spread copies via networks.

Class: Email-Worm

Email-Worms spread via email. The worm sends a copy of itself as an attachment to an email message or a link to its file on a network resource (e.g. a URL to an infected file on a compromised website or a hacker-owned website). In the first case, the worm code activates when the infected attachment is opened (launched). In the second case, the code is activated when the link to the infected file is opened. In both case, the result is the same: the worm code is activated. Email-Worms use a range of methods to send infected emails. The most common are: using a direct connection to a SMTP server using the email directory built into the worm’s code using MS Outlook services using Windows MAPI functions. Email-Worms use a number of different sources to find email addresses to which infected emails will be sent: the address book in MS Outlook a WAB address database .txt files stored on the hard drive: the worm can identify which strings in text files are email addresses emails in the inbox (some Email-Worms even “reply” to emails found in the inbox) Many Email-Worms use more than one of the sources listed above. There are also other sources of email addresses, such as address books associated with web-based email services.

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Platform: VBS

Visual Basic Scripting Edition (VBScript) is a scripting language interpreted by Windows Script Host. VBScript is widely used to create scripts on Microsoft Windows operating systems.


Technical Details

Type: Email Worm
Platform: MS Windows with Internet Explorer 5.0, MS Outlook 98/2000 or MS Outlook Express

This is an Internet virus-worm that spreads via the Internet as infected e-mail messages. The worm arrives as a message with no attachment, and the worm uses several tricks to activate its code directly from the message body. When this message is opened, the worm code takes control, gains access to system resources (disk files and system registry), processes the Outlook address book, and sends infected messages to these addresses (in a similar way that the Macro.Word97.Melissa virus does).

This is the first known modern Internet worm that spreads its copies with no attached data. As is the case with other Internet worms, a user must open the attachment in order to activate the worm's routines, which take control at the moment the message itself is opened.

The Deceptions

To spread its copies, this worm uses two means of deception. The first one is the MS Outlook feature allowing the creation of messages in HTML format. HTML messages may contain scripts that will be automatically executed at the moment the HTML message is being displayed (user opens the message). The worm uses this feature to run its code when the infected message is opened.

To spread its copies further and to bypass Internet Explorer security, the worm uses another trick. At the moment, this is termed the "Scriptlet.Typelib" security vulnerability.

This security breach allows HTML scripts to create disk files. The worm uses this breach to create a HTA-file (HTML Applications, new type appeared with IE5), which contains the main worm code. This file is created in the Startup Windows folder, and as a result, it is activated upon the next Windows startup. Being run as a local disk file, the worm's script in this HTML gains access to disk files and resources without any Internet Explorer security warning messages, connects to the Outlook address book, and spreads itself.

Technical details

When a user opens an infected message, the worm script embedded into this message body is automatically activated and executed by MS Outlook. This script (by using security breach) creates the "UPDATE.HTA" file in the "C:WINDOWSSTART MENUPROGRAMSSTARTUP" directory. This is the same file the worm tries to create in the "C:WINDOWSMENU INICIOPROGRAMASINICIO" directory (Spain Windows default name).

This "UPDATE.HTA" file contains the main worm code. It will be executed upon the next Windows startup, because of its location in the Startup folder. The worm has a minor bug here: it assumes that Windows is always installed in the C:WINDOWS directory. If this is not the case, the worm cannot create its file and fails to replicate further.

When the UPDATE.HTA file is executed, the worm runs the Outlook application in a hidden window and creates a new message to all recipients from the Outlook address book in the same way as the "Melissa" virus does. This new message has the HTML format and contains the worm's script in the body. The message subject is "BubbleBoy back!", and the text body appears as follows:

 The BubbleBoy incident, pictures and sounds

After this message has been sent, the worm creates the following in the system registry key in order to prevent duplicate messages from being sent:

 "HKEY_LOCAL_MACHINESoftwareOUTLOOK.BubbleBoy" = "OUTLOOK.BubbleBoy 1.0 by Zulu"

At the end, the worm leaves, on the screen, a window with the following text inside:

  System error, delete "UPDATE.HTA" from the startup folder to solve this

The worm also changes the Windows registration data (this routine is executed at the moment the UPDATE.HTA script takes control):

  RegisteredOwner = "BubbleBoy"
  RegisteredOrganization = "Vandelay Industries"


Microsoft has released an update that eliminates security the "Scriptlet.Typelib" vulnerability. We strongly recommend you visit and install this update.

If you do not use any HTML applications (HTA-files), there is another way to prevent infection by viruses of this type (the worms and viruses that use the "Scriptlet.Typelib" security vulnerability). It is necessary to remove the file association for the .HTA extension. To do this, you have to follow several steps:

  1. Double click the "My Computer" icon on the desktop.
  2. In the open window, choose menu "View" -> "Options...".
  3. On the "File Types" tab in the "Registered file types" listbox, select the "HTML Applicaton" item.
  4. Click the "Remove" button and confirm action.
  5. Close options dialogue box.

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