Virus Encyclopedia

Welcome to the Virus Encyclopedia of Panda Security.


Threat LevelModerate threat
DistributionNot widespread


Chir.B activates when the attachment is run. From that moment, the worm has the following effects:

  • It infects files with the following extensions: EXE, SCR, HTM and HTML.
  • On the first day of each month, it overwrites the first 4,660 bytes of files with the following extensions: ADC, R.DB, DOC and XLS.

Infection strategy 

Chir.B creates the following files:

  • RUNOUCE.EXE, in the Windows system directory. This file is a copy of the worm.
  • README.EML, in the directories in which the worm finds and infects files with an HTM and/or HTML extension. This file contains the worm's code in MIME format.

Chir.B creates the following entry in the Windows Registry:

  • HKEY_LOCAL_MACHINE\ Software\ Microsoft\ Windows\ CurrentVersion\ Run
    Runonce = %sysdir%\ runouce.exe

    where %sysdir% is the system directory.
    By creating this entry, Chir.B ensures that it is run whenever Windows is started.

Means of transmission 

Chir.B spreads itself via e-mail. It follows the routine below:

  • It reaches the computer in an e-mail message with the following characteristics:

    Sender: one of the following:

    %sender's name% is coming!

    Message: it does not contain any text.

  • It activates when the attachment is run.
  • It sends itself out to the e-mail addresses it gets from the infected user's Address Book.