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Anito.A


First posted on 02 April 2007.
Source: SecurityHome

Aliases :

Anito.A is also known as Worm:W32/Anito.A, Email-Worm:W32/Anito.A.

Explanation :

The 'Email-Worm:W32/Anito.A' is an e-mail worm. It sends out e-mail messages with a URL to a malicious file that contains the recently discovered 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 and a trojan downloader. It infects html files with a small script that downloads a file with a recently discovered ANI exploit. The worm also spreads to remote drives, modifies HOSTS file and downloads more malicious files onto an infected computer.

Email-Worm:W32/Anito.A

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

[HKCUSoftwareMicrosoftWindowsCurrentVersionRun]
"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 2 remote threads that create mutexes named 'MyDownload' and 'MyInfect'.

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


The worm downloads and runs additional files, replaces 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 e-mail messages. It reads SMTP server settings from a downloaded configuration file or uses hardcoded settings (the 'smtp.sohu.com' server is used in this worm variant). The e-mail 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.

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 beside the file size increase, this change remains unnoticed to a user.

In addition the worm scans files with the following extensions:


and inserts a small script code into them. 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 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 Windows System folder and creates a startup entry for the copied file in the Registry:

[HKCUSoftwareMicrosoftWindowsCurrentVersionRun]
"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 2 remote threads that create mutexes named 'MyDownload' and 'MyInfect'.

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


The worm downloads and runs additional files, replaces 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 HOSTS file, access is blocked to the following websites:


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 beside 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.

Last update 02 April 2007

 

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