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

Yanker is a very dangerous multicomponent worm-virus that spreads through via the internet as an RAR archive attached to infected emails.

Infected emails contain:

 Subject: Hi,my new webpage ;o) 
 E-mail body: Hi: 
 Here is my new webpage.Please check it,and give Me some Advice. 
 Attachment name: webpage.rar 

The RAR archive contains the file webpage.htm and a subcatalogue named images where the main components of this virus are stored:

folder.htt (controls MS Explorer file and folder display settings - attributes: system/hidden) 
main_59.exe (dropper file, written in Delphi, packed by UPX (57KB), attributes: system/hidden) 
main_60.exe (PSW.PassDumper, packed with UPX (20k) - attributes: system/hidden) 

The images folder also contains several harmless files in various formats, such as gif, css and more. These files are components of a webpage.

After unarchieving the infected RAR file the yanker worm can gain control of a user's system in two ways: when the webpage.htm file is opened or when the images folder is viewed using MS Explorer.

However, in both cases the yanker worm utilizes the same CodeBaseExec exploit, attached to the end of the files to launch itself. The file (program) main_59.exe runs without victim users being able to notice anything.

The main_59.exe program ascertains the current ip address of the infected computer and stores it in a txt file (ip.txt). Then it extracts and launches the worm's main component yankee.vbs - a file 4KB in size and written using Visual Basic Script. Simultaneously, the worm checks the system registry for the follwing key string:


If this string already exists, the worm ceases all activities.

The yankee.vbs script does the following:

  • Sends the ip.txt file with the infected computer's IP address and all passwords found in the system (using PassDumper) to the following e-mail address: 
  • Sends its "webpage.RAR" archive to all the addresses found in the MS Outlook address book.
  • Writes the following key string into the Windows System Registry:
  • Deletes all accessible non-system folders on hard and removable drives.

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