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

This is "LoveLetter" -like Internet worm spreading via e-mail by sending infected messages from infected computers. While spreading, the worm uses MS Outlook and sends itself to all addresses that are stored in the MS Outlook Address Book.

The known worm version has a mistake (one instruction is mistyped), and the worm is not able to spread its copies via e-mail messages. In addition to this, the mistake may be easily fixed, and the worm will be able to spread.

The worm is able to propagate through a local network. To do this, the worm enumerates network resources and copies itself to there. The worm is not able to activate itself on a remote computer, and infects it only in case the worm copy is occasionally run by a user.

The worm itself is a VBS script program.

The worm arrives as an e-mail message with:

Subject: I'am missing U
Message body: Could u remember me ?
Attachment name: Y072QWV.VBS

Upon being activated by a user, the worm copies itself to the Windows system directory with the same name (Y072QWV.VBS) and registers this copy in the auto-run section in the system registry:

"Y072QWV" = %Windir%Y072QWV.VBS

where "Windir" is the name of Windows system directory.

The worm then spreads through a local network by copying its "Y072QWV.VBS" file to the root directory on drives shared for writing.

To send infected messages, the worm connects to MS Outlook, obtains all addresses from the address book and sends to there its messages (the subject, body and attachment name are the same as listed above).

Because the worm registers itself in the auto-run registry section, it is activated upon each Windows boot-up, but it does not spread by e-mail messages each time it is run. The worm has a counter that is stored in the Windows registry:


where "number" is the number of starts (upon each start, the worm increases this counter). When the counter reaches 20, the worm resets it to zero and then runs an Outlook infection routine. Otherwise, the worm skips it.

As a result, the worm sends infected messages only upon the first run (being activated from an infected message), and upon each 20th reboot. The local network spreading routine is activated each time the worm starts.

The worm has a feature that makes its detection a little bit more difficult. All text strings in the worm code are slightly encrypted, and in case of need, the worm decrypts and uses them.

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