FRISK Software International


Summary of W32/Frethem@mm
Alias: I-Worm.Frethem.A
Discovered: 13 Jun 2002
Definition files: 13 Jun 2002
 
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Brief description
Technical description
Removal Instructions

Brief Description
There are 12 different variants of Frethem worm known so far (A-L). The K and L variants of the worm became widespread in the middle of July 2002. See the description of these variants below.


Technical Description

VARIANT: Frethem.A

Frethem is a mass-mailer worm that started to spread on June 11th. The worm arrives in an e-mail as an attachment. When the attachment is opened it copies itself to the user's Startup folder as 'setup.exe'. After the installation it collects e-mail addresses from the Windows Address Book and files with '*.DBX' extensions. It uses it's own SMTP engine to send infected messages. All the information needes to send e-mail is collected from the registry. The worm uses the user's account data that includes the SMTP server name, e-mail address, etc. This way the infected message will look like it was sent by the user.

The message sent by Freethem.A looks like this:

Subject: Re: Do your Windows looks like Windows XP?
          I have found very nice desktop themes!


 Body:


 Hello!


 Do you like modern design of new Windows XP?! I have found FREE
 and easy to use desktop themes!


 You can open attach with web site and samples! Enjoy it!!!


 Attachment: www.freethemes.com

VARIANT: Frethem.E

Messages sent by Freethem.E look like this:

This variant uses one MIME vulnerabilty in Internet Explorer to execute the attachment automatically when the e-mail is opened. This vulnerability is fixed and a patch for it is available on Microsoft site:

VARIANT: Frethem.K

Frethem.K is a new variant of Frethem worm that appeared in the middle of July 2002. This worm variant is close to Frethem.E variant, but it has some additional features. The worm's file is packed with PE-Pack and UPX file compressors and is about 47 kilobytes long.

The worm sends itself from an infected computer as with the following message:


Subject: 

	Re: Your password!

Body: 

	ATTENTION!


	You can access
	very important
	information by
	this password


	DO NOT SAVE
	password to disk
	use your mind


	now press
	cancel


	()

Attachment: 

	decrypt-password.exe
	password.txt

The executable attachment contains the worm's body. The 'password.txt' attachment contains the following text:


Your password is W8dqwq8q918213

The worm installs itself to system as TASKBAR.EXE and creates a startup key in System Registry to make this file start every time a user logs on. Also the worm copies itself as SETUP.EXE to \Start Menu\Programs\Startup\ folder.

To remove the worm from a system, all its files should be deleted. Also it is recommended to delete all infected messages from e-mail databases and to apply the latest security patches to Microsoft e-mail browsers.

VARIANT: Frethem.L

Frethem.L is another new variant of Frethem worm that appeared in the middle of July 2002. This worm variant is very close to Frethem.K variant. The worm's file is packed with PE-Pack and UPX file compressors and is about 48 kilobytes long. The worm sends itself the same way that the Frethem.K variant does, see the description above.



Removal Instructions
The above described variants of Frethem copy themselves to the user's startup folder as 'setup.exe' and introduce no other changes in the system configuration. This makes the removal easy. The worm's process can be killed from the task manager, the process is called 'Setup'. After this the worm can be deleted from the Startup folder.

[Analysis: G. Erdelyi, A. Podrezov; F-Secure Corp.; June 13th - July 15th, 2002]
 


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