Yanz is an mass-mailing worm. It sends email messages that contain texts and attachment names related to the Asian singer Stefanie Sun (Yanzi). The worm can also spread to shared folders of local network and peer-to-peer clients.
Once detected, the F-Secure security product will automatically disinfect the suspect file by either deleting it or renaming it.
The worm's file is a PE executable file about 102 kilobytes long. The file is not packed.
Installation to system
When the worm's file is run for the first time, it shows a fake messagebox:
Then the worm copies itself to Windows System directory as LSASSS.EXE and as YANZI.EXE and creates a startup key for the first file in System Registry:
[HKLM\Software\Microsoft\Windows\CurrentVersion\Run] "Microsoft Kernel" = "%WinSysDir%\lsasss.exe"
where %WinSysDir% represents Windows System folder, for example 'c:\windows\system32' for default Windows XP installation.
Also the worm creates a ZIP archive named YanZi.zip with the worm's file named 'Sun YanZi.pif' in Windows folder. The worm uses 'store' method to create a ZIP archive meaning that the worm's file inside the archive is not compressed.
The worm creates a short HTML file named 'sun_yanzi.htm' in the current directory and writes 'Sun-Yanzi' text string there.
Additionally the worm creates 2 base64-encoded files in Windows System folder:
The first file is a base64-encoded copy of the worm, the second one is a base64-encoded copy of the worm in a ZIP archive. These files are used during spreading of the worm in e-mails.
The worm creates a mutex with the name 'Sun YanZi - forever'.
Spreading in e-mails
Before spreading the worm reads user's Address Book and scans a hard drive to harvert victims' e-mail addresses. The worm scans files with the following extensions:
The worm ignores e-mail addresses if they contain any of the following substrings:
The worm sends e-mails with different subjects, body texts and attachment names. The subject of an infected e-mail is selected from the following variants:
- SuN YanZi
- Sun-YanZi Mp3
- Free MP3
- Love and SuN YanZi
- Forever Sun Yanzi
The body text of an infected e-mail is selected from the following variants:
- I don't want anything. I want to see Sun YanZi
- My Favourite is Sun YanZi.
- I want to meet Sun YanZi. I am loving Sun-YanZi Magic.
- You must to listen Sun-Yanzi. I am enjoying to listen Sun YanZi.
The attachment is either a ZIP archive with the worm's executable file or the worm's executable file itself. The name of an infected attachment is selected from the following variants:
The extension of an infected attachment can be:
Spreading to shared folders
The worm scans all available hard drives and ram disks. If it finds a folder with the name that contains 'shar' substring, it copies itself there with the following names:
- Sun YanZi.avi.exe
- Sun YanZi.mpg.exe
- Sun YanZi.mpeg.exe
- Sun YanZi - Shen Qi.exe
- Sun YanZi - I am not sad.mp3.exe
- Sun YanZi - Leave me alone.mp3.exe
- Sun YanZi - forever.mp3.exe
- Stephan YanZi.Mp3.exe
This way the worm can spread to shared folders of P2P (peer-to-peer) clients and to local network.
The worm has a simple backdoor that listens on TCP port 67. It allows to download and run executable files from Internet.
During its installation cycle the worm kills the following processes: