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: Win32

Win32 is an API on Windows NT-based operating systems (Windows XP, Windows 7, etc.) that supports execution of 32-bit applications. One of the most widespread programming platforms in the world.


Technical Details

This is a multi-component Internet-worm infecting Win32 machines and spreading in e-mail messages as an attached EXE file. The worm has several components, and is able to "upgrade" itself from an Internet Web site.

There are two principal worm components: Loader and Main component.

The Loader is a Windows EXE file about 25K in size (it is compressed by a UPX PE EXE file-compression utility, which being decompressed reaches about 70K in size). When the loader is activated on a computer (being run from e-mail attach), it registers itself as a hidden process (service), copies itself to the Windows system directory with the name GDI32.EXE, and registers in the auto-run system registry key:

GDI = WinSystemGDI32.EXE

where "WinSystem" is the Windows system directory name. As a result, the worm Loader then is executed upon each Windows startup. Note that there are standard Windows components in this directory: GDI.EXE and GDI32.DLL. The worm uses the GDI32.EXE name to disguise itself in a standard Windows environment.

To hide its activity, the worm then displays the fake error message:

FileName n' est pas une application Win32 valide.

where FileName is the actual file name the worm was started from.

The worm then activates the main procedure that obtains and executes the Main component. It enters the Web page and obtains several files from there:

  • LASTVERSION.TXT - a text file with the number of the latest worm version available there. If there is no new version, the worm exits.
  • nn.ZIP - latest version of worm Main component, "nn" is defined in LASTVERSION.TXT.
  • GATEWAY.ZIP - latest version of worm Loader component.

The nn.ZIP and GATEWAY.ZIP files are not actually archives, but an encrypted Windows EXE file. The worm Loader decrypts them, copies to the Windows directory and spawns. As a result, the Main component is activated on the computer.

The Main worm component is the Windows EXE file about 40K in size (it is compressed by a UPX PE EXE file-compression utility, which being decompressed reaches 120K in size). It is installed to the Windows directory with the GDI32A.EXE name and is registered in the system registry in a similar way as described above for the virus loader. The main components then, depending on some conditions, open the Windows Address Book, obtain Inet addresses from there and send infected e-mail messages. In the known worm version, these messages have:

Subject: Choose your poison
Attached file name: girls.exe

The Main worm component also has Backdoor abilities to watch at infected computer and run its resources from remote host machine.

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