Threat Description



Aliases:Yaha.K!e2a2, W32/Lentin.H@mm, Yaha.M, I-Worm.Lentin.h


Yaha.K is a Windows massmailer, which randomly composes its email subject,body and attachment name.


Automatic action

Once detected, the F-Secure security product will automatically disinfect the suspect file by either deleting it or renaming it.


You may wish to refer to the Support Community for further assistance. You also may also refer to General Removal Instructions for a general guide on alternative disinfection actions.

Eliminating a Local Network Outbreak

If the infection is in a local network, please follow the instructions on this webpage:

Technical Details

UPDATE (2002-12-30 22:30 GMT)

F-Secure is upgrading the Yaha.K e-mail worm to level 2 because it has been reported from several different countries. Yaha.K is a Windows massmailer, which randomly composes its email subject, body and attachment name.

UPDATE (2002-12-22 23:30 GMT)

A new variant of the Yaha virus family was found on Sunday the 22nd of December, 2002.

This version, also known as Yaha.M, is a massmailer - like the others.

E-mails sent by this version talk about "Enjoy this friendship Screen Saver and Check ur friends circle..." etc.

To block the virus, strip attachments ending with .SCR and .EXE and .COM at your firewall.

Technical Description

When run, the worm installs itself to system by copying its file to Windows System directory 3 times with the following names:

  • tcpsvs32.exe
  • nav32_loader.exe
  • WinServices.exe

Then the worm creates a startup key for WinServices.exe file in System Registry:

  • [HKLM\Software\Microsoft\Windows\CurrentVersion\Run] "WinServices" = "%WinSysDir%\WinServices.exe"
  • [HKLM\Software\Microsoft\Windows\CurrentVersion\RunServices "WinServices" = "%WinSysDir%\WinServices.exe"

The %WinSysDir% represents Windows System directory name. Also the worm modifies the default EXE file startup key:

  • [HKCR\exefile\shell\open\command] @ = "%WinSysDir%\nav32_loader.exe "%1"%*"

The worm creates several threads that refresh its Registry keys and continuously restore worm's files if they are deleted from a hard drive. One of the threads kills processes with the following names:

  • CFINET32
  • LOCKDOWN2000
  • AVP32
  • VSHWIN32
  • NAVAPW32
  • NAVW32
  • NSCHED32
  • SCAN32
  • TDS2-98
  • TDS2-NT
  • RESCUE32
  • NAVLU32
  • PVIEW95
  • F-PROT95
  • PCCWIN98
  • IOMON98
  • FP-WIN
  • NVC95
  • _AVP32
  • _AVPCC
  • NOD32
  • NRESQ32
  • NSCHED32
  • NAVAPW32
  • NAVLU32
  • NAVW32
  • _AVPM
  • N32SCANW
  • VET95
  • SWEEP95
  • VSHWIN32
  • PCCWIN98
  • F-AGNT95
  • ACKWIN32

The worm looks for e-mail addresses in Windows Address Book, cache folders of NET and MSN messengers and in Yahoo Messenger profile folders.

Then the worm sends itself to all found e-mail addresses. The worm composes several different types of e-mails. In those messages subjects, bodies and attachment names are correlated.

A subject of an infected e-mail can be one of the following:

  • Sample Screensavers
  • Project
  • Free Screensavers 4 U
  • Patch for Klez.H
  • Patch for Klez.H
  • Patch for Elkern.gen
  • Lovers Corner
  • Things to note
  • Wanna be friends ?
  • Freak Out
  • WWE Screensavers
  • Free Screensavers
  • Free XXX
  • Free Screenavers of Love
  • Who is your Valentine
  • Are you beautiful
  • Need money ??
  • Wanna be friends ??
  • Wanna be friends ??
  • Free Demo Game
  • Demo KOF 2002
  • Play KOF 2002 4 Free
  • Wanna Rumble ??
  • Wanna Brawl ??
  • The King of KOF
  • Sample KOF 2002
  • Wanna be friends ??
  • Wanna Hack ??
  • Feel the fragrance of Love
  • Free Screensavers
  • Free rAVs Screensavers
  • XXX Screensavers
  • Jenna 4 U
  • Screensavers from Club Jenna
  • Wanna be my sweetheart ??
  • Whats up
  • World Tour
  • One Hacker's Love
  • One Virus Writer's Story
  • Visit us
  • Wanna be a HE-MAN
  • We want peace
  • Free Screensavers 4 U
  • XXX Screensavers 4 U
  • Hardcore Screensavers 4 U
  • Sample Playboy
  • Check it out
  • Check it out
  • Check it out
  • Sexy Screensavers 4 U
  • Are you a Soccer Fan ?
  • Wanna be like a stone ?
  • I Love You..
  • Learn SQL 4 Free
  • Free Win32 API source
  • Are you the BEST

An infected attachment name can be one of the following:

  • Love.scr
  • Project.exe
  • Romantic.scr
  • Cupid.scr
  • Notes.exe
  • MyPic.scr
  • FreakOut.exe
  • THEROCK.scr
  • Britney_Sample.scr
  • zXXX_BROWSER.exe
  • Love.scr
  • Valentines_Day.scr
  • Beautifull.scr"
  • Ways_To_Earn_Money.exe
  • MyProfile.scr
  • My_Sexy_Pic.scr
  • KOF.exe
  • King_of_Figthers.exe
  • KOF2002.exe
  • KOF_The_Game.exe
  • KOF_Demo.exe
  • KOF_Sample.exe
  • KOF_Fighting.exe
  • MyPic.scr
  • Hacker.scr
  • Romeo_Juliet.scr
  • Free_Love_Screensavers.scr
  • Ravs.scr
  • zDenka.scr
  • Jenna_Jemson.scr
  • Sexy_Jenna.scr
  • Sweetheart.scr
  • up_life.scr
  • World_Tour.scr
  • Hacker_The_LoveStory.scr
  • VXer_The_LoveStory.scr
  • Services.scr
  • Body_Building.scr
  • Peace.scr
  • Screensavers.scr
  • xxx4Free.scr
  • Hardcore4Free.scr
  • Playboy.scr
  • Plus2.scr
  • Plus6.scr
  • Real.scr
  • Sex.scrSoccer.scr
  • Stone.scr
  • I_Love_You.scr
  • SQL_4_Free.scr
  • Codeproject.scr
  • The_Best.scr

An infected message body can contain one of the following:

 The attached product is send as a part of our official campaign 
 for the popularity of our product.  
 You have been chosen to try a free fully functional sample of our 
 product.If you are satified then you can send it to your friends. 
 All you have to do is to install the software and register an account 
 with us using the links provided in the software. Then send this software 
 to your friends using your account ID and for each person who registers 
 with us through your account, we will pay you $1.5.Once your account reaches 
 the limit of $50, your payment will be send to your registration address by 
 check or draft.  
 Please note that the registration process is completely free which means 
 by participating in this program you will only gain without loosing anything. 
 Best Regards, 
 Klez.H is the most common world-wide spreading worm.It's very 
 dangerous by corrupting your files. Because of its very smart 
 stealth and anti-anti-virus technic,most common AV software 
 can't detect or clean it.  
 We developed this free immunity tool to defeat the malicious virus.  
 You only need to run this tool once,and then Klez will never 
 come into your PC 
 Looking for some Hardcore mind boggling action ? 
 Install the attached browser software and browse 
 across millions of paid hardcore sex sites for free.  
 Using the software you can safely and easily browse 
 across most of the hardcore XXX paid sites across the 
 internet for free. Using it you can also clean all 
 traces of your web browsing from your computer.  
 Note:The attached browser software is made exclusivley 
 for demo only. You can use the software for a limited 
 time of 35 days after which you have to register it 
 at our official website for its furthur use.  
 I just came across your email ID while searching in the Yahoo profiles. 
 Actually I want a true friend 4 life with whom I can share my everything.  
 So if you are interested in being my friend 4 life then mail me.  
 If you wanna know about me, attached is my profile along with some of my 
 pics. You can check and if you like it then do mail me.  
 I will be waiting for your mail.  
 Best Wishes 
 Your Friend.. 
 This E-Mail is never sent unsolicited. If you receive this 
 E-Mail then it is because you have subscribed to the official 
 newsletter at the KOF ONLINE website.  
 King Of Fighters is one of the greatest action game ever made.  
 Now after the mind boggling sucess of KOF 2001 SNK proudly 
 presents to you KOF 2002 with 4 new charecters.  
 Even though we need no publicity for our product but this 
 time we have decided to give away a fully functional trial 
 version of KOF 2002. So check out the attached trial version 
 of KOF 2002 and register at our official website to get a free 
 copy of KOF2002 original version 
 Best Regards, 
 Admin,KOF ONLINE..  

Also the worm can compose e-mails with the following subjects:

  • Hi
  • Hello
  • Check this shit
  • hey check it yaar
  • Who is ur Best Friend
  • make ur friend happy
  • True Love
  • Looking for Friendship
  • Let's Dance and forget pains
  • love speaks from the heart
  • Say 'I Like You' To ur friend
  • Need a friend?
  • war Againest Loneliness
  • How sweet this Screen saver
  • love speaks from the heart"
  • Shake it baby
  • The world of Friendship
  • Check ur friends Circle
  • Wowwwwwwwwwww check it
  • Are you looking for Love
  • Learn How To Love
  • Find a good friend
  • to ur friends
  • to ur lovers
  • U realy Want this
  • The Hotmail Hack
  • You are so sweet
  • I Love You
  • One Hacker's Love
  • I am in Love
  • Are you in Love

The composed e-mails can have worm's attachments with one of the following names:

  • funny.scr
  • friendship_funny.scr
  • colour_of_life.scr
  • life.scr
  • Best_Friend.scr
  • Friend_Happy.scr
  • True_Love.scr
  • GC_Messenger.exe
  • dance.scr"
  • I_Like_You.scr
  • Friend_Finder.exe
  • Be_Happy.scr
  • Sweet.scr
  • Love.scr
  • shake.scr
  • world_of_friendship.scr
  • friendship.scr
  • love.scr
  • hotmail_hack.exe

The composed e-mail body can be one of the following:

 did u always dreamnt of hacking ur friends hotmail account..  
 finally i got a hotmail hack from the internet that really works..  
 ur my best friend thats why sending to u.. 
 check it..just run it..enter victim's address and u will get the pass. 
 check the attached love screensaver 
 and feel the fragrance of true love.. 
 check the attached screensaver.. 
 its really wonderfool.. 
 i got it from 
 check ur friends circle using the attached friendship screensaver.. 
 check the attached screensaver 
 and if u like it send it to all those you consider 
 to be true friends... if it comes back to you then 
 you will know that you have a circle of friends.. 
 check the attached screensaver 
 and enjoy the world of friendship.. 
 are u in a rocking mood... 
 check the attached scrennsaver and start shaking.. 
 Check the attached screensaver.. 
 Are you lonely ??.. 
 check the attached screensaver and 
 forget the pain of loneliness 
 Looking for online pals.. 
 check the attached friend finder software.. 
 sending you a screensaver.. 
 check it and let me know how it is... 
 Check the attached screensaver 
 and feel the fragrance of true love... 
 I just got this wonderfull screensaver from 
 Just check it out and let me know how it is.. 
 I just came across it.. check out.. 
 Are you one of those unfortunate human beings who are desperately 
 looking for friends.. but still not getting true friends with whom 
 you can share your everything.. 
  anyway you wont feel down any more cause GC Chat Network has brought 
 up a global chat and online match making system using its own GC 
 Messenger. Attached is the fully functional free version of GC 
 Instant Messenger and Match Making client.. 
 Just install, register an account with us and find thousands of online 
 pals all over the world.. 
 You can also search for friends by specific country,city,region etc. 
  Regards Admin, 
 GC Global Chat Network System.. 
 So you think you are in love.. 
 is it true love ? you may think right now that you are in 
 true love but it is certainly possible that it is nothing 
 but a mere infatuation to you.. 
  anyway to know yourself better than you have ever known check 
 the attached screensaver and feel the fragrance of true love.. 
 Hey pal, 
 you know friendship is like a business... 
 to get something you need to give something.. 
 though its not that harsh as business but to 
 get love and care from your friends you need to give 
 love,care and respect to your friends.. right 
  check the attached screensaver and you will learn how to 
 make your friends happy.. 
 Its quite obvious that in our life we have numerous friends 
 but.. BUT Best Friend can only be ONE.. right 
 so can you decide who is your best friend 
 i guess not.. cause mostly you will find that your best friend 
 wont care about u like somebody else.. 
  anyway i found one way to find who is my best friend.. 
 check it.. 
 just check the attached screensaver.. answer some questions 
 in it and also ask your best friend to answer the questions.. 
 ..then you will know more about him.. 
 Hey pal, 
 wanna have some fun in life... 
 feel like life is too boring and monotonous.. 
 check the attached screensaver and bring colours 
 to your black & white life.. :) 
 I just came across this funny screensaver.. 
 sending it to u.. hope u like it.. 
 check out and die laughing.. :) 

It should be noted that some messages might not be displayed correctly due to typos in the tag that the author uses to separate text lines.

The worm fakes sender's name and e-mail address by substituting it with data that is hard-coded in its body. It should be noted that many names and e-mails belong to real persons or companies.

Below is the list of senders names that the worm uses:

  • Love Inc.
  • Jericho
  • Romantic Screensavers
  • Trend Micro
  • Norton Antivirus
  • McAfee Inc.
  • Cupid
  • Jonathan
  • Susan
  • Noopman
  • The Rock
  • zporNstarS
  • Lovers Screensavers
  • Valentine Screensavers
  • American Beauty
  • John Vandervochich
  • Ross Anderson
  • Jasmine Stevens
  • Ralph Jones
  • Clark Steel
  • Kyo Kusanagi
  • Iori Yagami
  • Terry Bogard
  • Omega Rugal
  • KOF Online
  • Cathy Kindergarten
  • Jaucques Antonio Barkinstein
  • Romeo &amp; Juliet
  • Screensavers of Love
  • Raveena Pusanova
  • Zdenka Podkapova
  • Jenna Jameson
  • Club Jenna
  • Veronica Anderson
  • Benting
  • Paul Owen
  • Nicolas Schwarzeneggar
  • Keanu Stevenson
  • Nomadic Screensavers
  • XXX Screensavers
  • Hardcore Screensavers
  • Playboy Inc.
  • Plus 2
  • Plus 6
  • Real Inc.
  • Sexy Screensavers
  • Super Soccer
  • Rocking Stone
  • me2K
  • SQL Library
  • Codeproject
  • Klein Anderson

And that is the list of e-mail addresses that the worm uses to fake the sender's e-mail address in an infected message:


The worm can change the default Internet Explorer startup page to point to one of these sites:


The worm tries to create a DoS (Denial of Service) attack on the website.

The worm also contains an internal text message from its authors. We are not going to show it here as it uses bad language and style.


Suspect a file or URL was wrongly detected? Submit a sample to our Labs for analysis

Submit Now

Give And Get Advice

Give advice. Get advice. Share the knowledge on our free discussion forum.

Learn More