Classification

Category: Malware

Type: Trojan-Dropper, Email-Worm

Aliases: Anito.A

Summary


This description is for two detections: Email-Worm:W32/Anito.A and Worm:W32/Anito.A.

Email-Worm:W32/Anito.A is an email worm and a file infector. It sends out email messages with a URL to a malicious file that contains the recently discovered (March/April 2007) ANI exploit. The worm also drops another malware, a worm and trojan-downloader that we detect as Worm:W32/Anito.A. This worm is similar to the one that we detect as Trojan-Downloader.Win32.Agent.bky and Worm.Win32.Diska.c.

Worm:W32/Anito.A is a worm, a file infector and a trojan-downloader. It infects HTML files with a small script that downloads a file with a recently discovered ANI file exploit. Also EXE files get infected. The worm also spreads to remote drives, modifies the HOSTS file, and downloads more malicious files onto an infected computer.

Removal


Automatic action

Based on the settings of your F-Secure security product, it will either automatically delete, quarantine or rename the detected program or file, or ask you for a desired action.

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About the product

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Submit a sample

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Technical Details


Email-Worm:W32/Anito.A

After the worm's file is run, it copies itself as sysload3.exe into the Windows System folder and creates a startup entry for the copied file in the Registry:

  • [HKCUSoftware\Microsoft\Windows\CurrentVersion\Run]"System Boot Check" = "%WinSysDir%/sysload3.exe"

This is done to ensure that worm starts every time Windows is loaded. After installation the worm starts Internet Explorer and Notepad and injects a part of its code into those processes. That code creates two remote threads that create mutexes named "MyDownload" and "MyInfect".

The first remote thread connects to the Internet and downloads a configuration file named css.css from a website. The file is saved locally with the name config.ini. The configuration file contains URLs to the following:

  • More malicious files that are downloaded and executed
  • Data to replace the local HOSTS file
  • An updated copy of the worm
  • A site to collect statistics about the worms spread

The worm downloads and runs additional files, replaces the Windows HOSTS file with the one downloaded from Internet, downloads an updated copy of itself, and opens a statistics URL in Internet Explorer.

Then this remote thread tries to send out email messages. It reads SMTP server settings from a downloaded configuration file or uses hard-coded settings (the "smtp.sohu.com" server is used in this worm variant). The email messages sent by the worm are in Chinese. They contain a URL to the HTML page that points to a file with the recently discovered ANI exploit. (March/April 2007).

The second remote thread creates and runs the original EXE file in case the worm started from an infected file. Then it scans local and remote drives from Z: to B: for files with .EXE extensions and infects them if their size is in the range of 10240 and 10485760 bytes. The worm prepends to the found EXE files and "borrows" their icons. So besides the file size increase, this change remains unnoticed to a user.

In addition the worm scans files with the following extensions:

  • .ASP
  • .ASPX
  • .HTM
  • .HTML
  • .JSP
  • .PHP

It inserts a small script code into such files above. The script points to a file located at the "macr.microfsot.com" website (notice the deliberate typo!). According to the reports there was a file with the recently discovered ANI exploit there. By the time of this description's creation the site was down.

Also, the worm attempts to copy itself to removable drives together with the autorun.inf file. As a result, when an infected removable media is inserted into a computer where autostart is enabled, the worm's file gets activated and a new infection round is started.

Worm:W32/Anito.A

After the worm's file is run, it copies itself as sysload3.exe into the Windows System folder and creates a startup entry for the copied file in the Registry:

  • [HKCUSoftware\Microsoft\Windows\CurrentVersion\Run]"System Boot Check" = "%WinSysDir%/sysload3.exe"

This is done to ensure that worm starts every time Windows is loaded. After installation the worm starts Internet Explorer and Notepad and injects a part of its code into those processes. That code creates two remote threads that create mutexes named "MyDownload" and "MyInfect".

The first remote thread connects to the Internet and downloads a configuration file named css.css from a website. The file is saved locally with the name config.ini. The configuration file contains URLs to the following:

  • More malicious files that are downloaded and executed
  • Data to replace the local HOSTS file
  • An updated copy of the worm
  • A site to collect statistics about the worm's spread

The worm downloads and runs additional files, replaces the Windows HOSTS file with the one downloaded from Internet, downloads an updated copy of itself, and opens a statistics URL in Internet Explorer. After the worm replaces the HOSTS file, access is blocked to the following websites:

  • 222.73.220.45
  • 55880.cn
  • 60.169.0.66
  • 60.169.1.29
  • 61.152.169.234
  • adnx.yygou.cn
  • cc.wzxqy.com
  • cool.47555.com
  • d.77276.com
  • d.qbbd.com
  • do.77276.com
  • down.97725.com
  • i.96981.com
  • ip.315hack.com
  • ip.54liumang.com
  • mmm.caifu18.net
  • wm,103715.com
  • www.18dmm.com
  • www.41ip.com
  • www.5117music.com
  • www.54699.com
  • www.54699.com
  • www.97725.com
  • www.9cyy.com
  • www.asdwc.com
  • www.baidulink.com
  • www.down.hunll.com
  • www.f5game.com
  • www.guazhan.cn
  • www.heixiou.com
  • www.hunll.com
  • www.my6688.cn
  • www.union123.com
  • www.wu7x.cn
  • www1.cw988.cn
  • xulao.com

The second remote thread creates and runs the original EXE file in case the worm started from an infected file. Then it scans local and remote drives from Z: to B: for files with .EXE extensions and infects them if their size is in the range of 10240 and 10485760 bytes. The worm prepends to the found EXE files and "borrows" their icons. So besides the file size increase, this change remains unnoticed to a user.

Also, the worm attempts to copy itself to removable drives together with the autorun.inf file. As a result, when an infected removable media is inserted into a computer where autostart is enabled, the worm's file gets activated and a new infection round is started.

It should be noted that previous versions of this worm appended a small script to HTML files. The script pointed to a website where the recently discovered ANI exploit was located. This particular worm variant does not infect HTML files.