Summary

Scold is a basic mass mailer discovered on the 11th of December 2003. It will send simple e-mails. The worm uses very simple tricks to try to avoid generic and heuristic detection by scrambling obvious text strings.

Disinfection

Removal of the file suffices to eliminate this threat from the system.

Additional Details

This worm was written in Visual Basic and packed with UPX. The packed executable has suffered no later modifications to make the unpacking process more difficult.

The size of the packed executable is 28160 bytes. Once unpacked it grows up to 61440 bytes long.

The worm author tried to avoid general detection methods by scrambling the main strings in the worm's code. Some of the text strings are reversed and other are written character by character.

Installation to system

The worm will copy itself to the Windows' System folder as "Warm.scr", whose path will be obtained by means of the GetSpecialFolder Method.

It will add an entry in the Windows Registry under:

 [HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run]
 "ExeName32"

to point to the "Warm.scr" file, so it's run as soon as Windows starts.

Spreading in e-mail.

The subject is one of the following:

 When It's Cold Outside She Gives Me Warm Inside
 Fw:When It's Cold Outside She Gives Me Warm Inside
 Re:When It's Cold Outside She Gives Me Warm Inside

The e-mail body will contain text from the following list:

 You will love this cute picture.
 Enjoy this great picture.
 Don't miss this cool picture.

Followed by some text like:

 Free Online Virus Scan.
 No viruses or suspicious files were found in the attached file.

The attachment will have the extension ".SCR"

It will send messages to all the addresses in the user's address book. It will also look for addresses in HTML files present in the computer's HD.

Detection

F-Secure Anti-Virus detects this worm using generic methods. Exact detection was published on December 11th, 2003 in update:

[FSAV_Database_Version]
Version=2003-12-11_01

Write-up: Ero Carrera, December 11th, 2003;

Technical Details: Ero Carrera, December 11th, 2003;