Virus Encyclopedia

Welcome to the Virus Encyclopedia of Panda Security.


Threat LevelModerate threat
DistributionNot widespread
Common name:Chir.B
Technical name:W32/Chir.B
Threat level:Low
Alias:I-Worm.Runouce.b,, Win32/ChiHack, PE_CHIR.B
Effects:  It overwrites files with certain extensions and exploits two vulnerabilities in Internet Explorer.

Affected platforms:

Windows 2003/XP/2000/NT/ME/98/95

First detected on:Aug. 1, 2002
Detection updated on:June 17, 2010
Proactive protection:
Yes, using TruPrevent Technologies

Brief Description 


Chir.B is a worm that reaches computers in an e-mail attachment called PP.EXE. The subject of this message consists of the sender's name followed by the text is coming!.

It is easy to get infected with this worm, as it activates automatically when the message is opened or just viewed through Outlook's Preview Pane.

In order to do so, it exploits two vulnerabilities: Exploit/iFrame and Exploit/MIME. These vulnerabilities allow files attached to e-mail messages to be run automatically.

This is a dangerous worm, as it infects files with the following extensions: EXE, SCR, HTM and HTML. Besides, Chir.B has destructive effects, as 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.

Visible Symptoms 


A clear indication that you have received Chir.B is a message with the following characteristics:

  • Sender: one of the following:
  • Subject:
    %sender's name% is coming!
  • Message: it does not contain any text.
  • Attachments: