F-Secure Virus Descriptions : WinExt

NAME:	WinExt
ALIAS:	I-Worm.WinExt, I-Worm.Trit

WinExt is an encrypted Internet worm. It usually appears as TRYIT.EXE file attached to email messages. This worm itself is Windows PE executable that is about 70Kb long.

When the worm is run it installs itself as WINEXT.EXE into Windows directory and modifies INI files or/and Registry to be run during all further Windows sessions. The worm also creates the additional WINEXT.DAT file in the same directory, and saves some data there. This data is used by the worm while spreading its copies.

After installation the worm sleeps for 1 hour and then launches its spreading routine. To spread itself the worm connects to MS Outlook by using MAPI functions, gets access to messages in Outlook database, and "answers" them with attached TRYIT.EXE file (worm's copy). The "answer" has the same subject with "Re:" prefix, and the message body is randomly selected from variants:

 Hi, *
 See You Soon

 Salut *,
 A+.

 A bientot.

 J'ai bien reçu ton message,
 je m'en occupe rapidement.
 En attendant, regardes le fichier joint.

where '*' is recipient's name.

The worm also seems to have backdoor capaabilities. It checks the messages for specific data, then gets "commands" from the message. There are few commands accepted by the worm: "Stop" - the worm deletes current mail message; "DeleteExe" - the worm uninstalls itself from system and some other commands.

The worm constantly checks system date and in August it removes itself from infected system. About 20 days before that (from 11th to 31st of July) the worm sends "Happy Birthday" congratulations to the email address "nathalie.paget@francetelecom.fr". These messages are randomly constructed from several variants:

 Bon anniversaire
 Happy birthday
 Bonjour Nathalie
 Coucou
 Hi Nathalie
 Bon anniversaire Nathalie
 Happy birthday Nathalie

 Salut Nathalie,
 Je te souhaite un bon anniversaire.

 Bon anniversaire
              /\_/\
         ____/ o o \
       /~____  ='= /
      (______)__m_m)

 Hi Nathalie,
 Happy birthday to you.

 Mille bisous pour ton anniversaire.

 Happy birthday Nathalie,
  O O
 0 * 0
  0 0'
     \/\
      \/

 Des milliers de fleurs pour ton anniversaire.

 Bonjour Nathalie,
 Je pense a toi pour ton anniversaire

 Tous mes voeux de bonheur

 Bisous,  Loutine
 A bientot    Loutine
 Tu me manques   Loutine
 See you soon   Loutine
 A+   Loutine
 :-)  Loutine
 :(   Loutine
 Je t'embrasse tres fort   Loutine
 Je t'aime   Loutine

The worm also has the "loutine@hotmail.com" email address in its body, but does not use it.

[Analysis: Eugene Kaspersky, AVP team]