The e-mails sent by Klez can have a wide variety of different
subject fields such as:
Subject:
Hi
Hello
How are you?
Can you help me?
We want peace
Where will you go?
Congratulations!!!
Don't cry
Look at the pretty
Some advice on your shortcoming
Free XXX Pictures
A free hot porn site
Why don't you reply to me?
How about have dinner with me together?
Never kiss a stranger
The message has no text in body and the attachment name is
random.
The worm part contains a hidden message targeted towards
anti-virus researchers. Most e-mail clients will not show this
message. It looks like this:
On some systems the worm is able to self-launch itself when an
infected e-mail is viewed (for example, with Outlook and IE 5.0
or 5.01). To do this the worm uses a known vulnerability in IE
that allows execution of an email attachment. This vulnerability
is fixed and a patch for it is available on Microsoft site:
The Klez worm copies itself to root directories of local and
network drives with a random name and with double extension, such
as .TXT.EXE.
This worm/virus combo apparently originated from Asia, possibly
China or Hong Kong. First infections were located early on the
morning of 26th of October, 2001.
Klez.d apperared in the wild on 11th of November, 2001.
This variant has a few changes compared to the previous versions.
First of all it looks for e-mail addresses in the user's
ICQ database files also. This means that anyone in the user's ICQ
contact list is a potential recipient of the worm.
Another change in the e-mail part is that the attachments can
now have EXE and PIF extension also. It was only EXE with the
previous versions.
When the worm is copied to the Windows system directory it's now
named as 'WinSvc.exe'. The same name is used in the registry run
key:
This version of the worm will try to locate and terminate processes
that contain the words like 'Nimda', 'CodeRed', 'Code Red',
'CodeBlue', 'Code Blue'.
It also has a string inside that is never displayed:
'I will try my best to kill some virus'
F-Secure Anti-Virus detects and stops both Klez and Elkern.
Detection was added with the update shipped on 26th of October
around 15 o'clock GMT. The update with detection for D variant
was published on 12th of November 09:00GMT.
F-Secure has created a special utility to disinfect Klez worm and
Elkern virus. The utility is available for download from ftp
site:
Klez.E is a new variant of Klez worm that was first discovered on
17th of January 2002. The worm is "version 2.0" according to its
author's classification and has several new features comparing to
the older variants. The worm still has bugs that remained from
previous versions.
The differences from the original version are as follows:
1. The worm installs itself to Windows System directory as
WINKxxxx.EXE file. The 'xxxx' can be 2-3 random letters. The worm
creates an autostarting key for its file in System Registry.
2. The worm now has file infection capabilities. When infecting
an EXE file, the worm overwrites it and creates a backup file
with the same name as the infected file, but with a random
extension with hidden, system and read-only attributes. When
the infected file is run, the worm extracts the original program
from a backup file with its original name plus 'MP8' and runs it.
After the program terminates, the worm deletes it. The worm
doesn't infect files with the following names:
EXPLORER
CMMGR
MSIMN
ICWCONN
WINZIP
This type of infection is called 'companion infection'.
3. The worm has network spreading capabilities. The worm
enumerates network resources and copies itself to remote drives
twice - once as an executable file with single or double
extension, and second time as a RAR archive that can have single
or double extension as well. The RAR archive contains the worm's
executable file with one of the following names:
setup
install
demo
snoopy
picacu
kitty
play
rock
The first extension of the RAR archive or of the worm's
executable can be:
The second or the only extension of the worm's executable file
can be:
.exe
.scr
.pif
.bat
The dropped RAR archive and worm's executable file name is either
random or belongs to a file, that a worm found on a host system.
So it can be for example QQ.PAS.EXE , KERNEL.MP3.PIF ,
DOCUMENT.SCR and so on.
4. The worm kills tasks of anti-virus and security software as
well as tasks of several other worms - Nimda, Sircam, Funlove and
CodeRed. The worm opens processes and looks for the specific text
strings there. If a specific text string is found in a process,
the worm terminates this process. The strings the worm looks for
are:
5. The worm removes autostarting Registry keys of security and
anti-virus software thus disabling this software or parts of it
completely on next Windows startup.
6. The worm affects anti-virus checksum files and ingegrity
checker databases with the following names:
7. The worm drops a new version of Elkern virus ("version 1.1"
according to author's classification) that is also known as
Win32.Klez.b. Please see Elkern description for more info, the
link to it is on the top of this page.
8. The worm can corrupt binary executables and data files.
9. The worm contains the following text strings that are never
displayed:
Win32 Klez V2.0 & Win32 Elkern V1.1,(There nick name is Twin Virus*^__^*)
Copyright,made in Asia,announcement:
1.I will try my best to protect the user from some vicious
virus,Funlove,Sircam,Nimda,CodeRed and even include W32.Klez 1.X.
2.Well paid jobs are wanted
3.Poor life should be unblessed
4.Don't accuse me.Please accuse the unfair sh*t world
10. The worm has a complex payload routine. It works as a
separate thread and constantly checks system date. If the month
number is odd (1, 3, 5, etc.) and the date is equal to 6 then the
worm proceeds further. It then checks if the month number is
equal to 7 (July) or 1 (January) and sets a special flag if it
is. Then the main payload routine is activated. It looks for all
files on all local and network drives. If the month is not 1 or 7,
the routine only affects files with the following extensions:
txt
htm
html
wab
doc
xls
jpg
cpp
c
pas
mpg
mpeg
bak
mp3
Otherwise all files are affected. The worm overwrites found files
with random data thus destroying their content.
11. E-mail messages sent by Klez.e are composed according to really
complex rules that makes possible of creating a large number of different
messages. It can create sentences from different parts like:
'The attachment is a very dangerous virus that spread trough e-mail.'
'The file is a special dangerous virus that can infect on Win98/Me/2000/XP.'
Around special dates special greeting messages are sent too. Like these:
'Happy Christmas'
'Happy New Year'
Here are screenshots of Klez.E worm when it arrives in e-mail:
Just like the other variants of Klez this one uses the Incorrect
MIME Header (MS01-020) vulnerabilty to send attachments that are
automatically executed when the message is opened. See the link
to Microsoft security advisory above.
Recipient e-mail addresses are collected from the Windows Address
Book as well as from ICQ user databases. The worm uses it's own
SMTP routines so it can send e-mail without an e-mail client.
Important Note: The e-mails sent by Klez.E worm often have faked
sender's address. The worm randomly picks sender's address from
web pages, ICQ databases or Windows Address Books. This means
that if you get Klez.E worm in e-mail, it's quite likely that it
was NOT sent to you by the person listed in the 'From' field of
e-mail message (sender's address).
Detection of Klez.E worm is available in the updates published on
17th of January 2002.
Disinfection of Klez.E worm can be performed with the special
tool that is available on our ftp site:
Klez.G worm appeared on 29th of January 2002. This variant is
very close to Klez.E variant. The worm drops Elkern virus 1.1,
identical to the one that was dropped by Klez.E variant. Only a
few differences have been noticed in G variant:
1. When an infected file is run, the worm extracts the original
file from a temporary file (created upon infection) with its name
plus its extension, adds EXE extension and runs it. For example
the preserved temporary file name is SYSTEM.CLF, so the worm will
create a new file called SYSTEMCLF.EXE with the code of the
original infected file and run it.
2. The author of the worm sends a 'message' to AV companies in
his worm's credits:
2.Pitiful AVers,can't Elkern 1.0 & 1.1 work on Win 2K&XP?Plz clear your eyes.
It should be noted that the Elkern virus works on Windows 2000
only due to dumb luck as there's a serious bug in the virus code
that usually makes it crash just after installation into memory.
The worm still corrupts a lot of system files including DLL and
VXD ones that often makes a system unusable after restart. The
corruption happens because the worm tries to preserve the
time/date stamp of a file it tries to infect and it saves this
value into EXE file header without bothering to check if it's a
PE, NE or LE header. So NE and LE headers get corrupted and a
file usually becomes unusable after that.
Like Klez.E variant, the new variant can send itself with empty
messages with one the following subjects:
how are you
let's be friends
darling
don't drink too much
your password
honey
some questions
please try again
welcome to my hometown
the Garden of Eden
introduction on ADSL
meeting notice
questionnaire
congratulations
sos!
japanese girl VS playboy
look,my beautiful girl friend
eager to see you
spice girls' vocal concert
japanese lass' sexy pictures
Also the worm sometimes sends messages pretending to be infection
removal tools from a few anti-virus companies. For example:
Subject: <virusname> removal tools
Body:
<virusname> is a dangerous virus that spread through email.
<av_company_name> give you the <virusname> removal tools
For more information,please visit http://www.<av_company_name>.com
The <av_company_name> can be 'Symantec', 'Mcafee', 'F-Secure' or
'Sophos'. The <virusname> can be 'W32.Elkern' or 'W32.Klez'. Do
not run attachments from such messages!
Also the worm can pretend to be a game, it can send itself
(usually as SETUP.EXE) with the a message:
This is a special humour game
This game is my first work.
You're the first player.
I expect you would like it.
The first and last lines can vary. This message will be displayed
only by e-mail clients that ignore IFrame trick used by the worm
to automatically launch itself from an e-mail message.
The worm can also send 'congratulations' on one of the following
holidays:
Christmas
New year
Saint Valentine
Allhallowmas
April Fools' Day
Lady Day
Assumption
Candlemas
All Souls' Day
Epiphany
Detection of Klez.G worm is available in the updates published on
30th of January 2002.
This worm variant appeared in the wild on 17th of April 2002. It
is quite close to E, F and G variants of Klez. The description of
this worm variant is available here:
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