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 Internet worm infects computer with installed Windows 9x and Internet Explorer 5.0 without Scriptlet.TypeLib hotfix (MS99-032). The worm spreads via E-mail by sending infected messages from affected computers. While spreading the worm uses MS Outlook and sends itself to all addresses that are stored in MS Outlook Address Book. The worm also has alternate spreading method that does not use Outlook at all.

The worm arrives to a computer as email message in HTML format. The subject of message may be vary. Message body has no visible text but contain script that is worm itself.

At the moment message is opening or displayed in preview pane, script activates and worm's code executing. At this moment ActiveX warning may appear on display:

An ActiveX control on this page might be unsafe to interact with other parts
of the page. Do you want to allow this interaction?
[YES] [NO]

Choosing [NO] will not allow the worm to execute.

Being activated worm drops some files that are worm's parts, gets access to Outlook and spreads using it, then searching on computer hard drive for email addresses, collects them and use in alternate spreading routine.

Composing infected message to send, the worm choosing subject from one of existing messages from Outlook Inbox. The worm also attaches HTML file with worm code. File name is name of one of attachments existing in inbox with added "(9 Kbytes).vbs". Thus, infected message contain worm code twice - in the message HTML body and in the attachment.

The worm adds itself to all signature files used by MS Outlook. This means every composed message in HTML format will contain worm code.

The worm replaces Internet Explorer start page with blank one. Four days after infection the worm replaces start page again with URL pointed to "".

The worm has alternate spreading method that does not use Outlook at all. This routine searches on local hard drive for files with extensions "txt", "na2", "wab", "mbx", "dbx" and "dat" (these are usual extensions for mail databases) and then searches and collects e-mail addresses in these files. Collected addresses then posted (using HTML form) to worm's author internet site. Special script on that site send infected messages directly from site to every address received. Such messages have same address in "From" and "To" fields and contain only HTML body with worm code inside. This alternate spreading method will not work as soon as worm author's site will be closed.

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