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Luder.A


First posted on 01 March 2007.
Source: SecurityHome

Aliases :

Luder.A is also known as Trojan-Downloader.Win32.Tibs.jy, Email-Worm.Win32.Luder.a, Luder.

Explanation :

Luder is an e-mail worm, a dropper for a trojan downloader and a file infector. The worm sends itself as attachment named 'postcard.exe' (or similar) in e-mail messages with the 'Happy New Year!' subject (or similar). The trojan downloader downloads and runs files from a website.

Infection of a system

After the worm's file is run, it copies itself to Windows System folder with ppl.exe name and creates startup keys for this file in Windows Registry:


where %WinSysDir% represents Windows System folder (usually C:WindowsSystem32). The worm also drops a trojan downloader file with a random name into Windows System folder and starts it.


Spreading in e-mails

Before spreading, the worm collects e-mail addresses from an infected computer. It locates and reads the WAB (Windows Address Book) file. The worm sends messages with the following characteristics:

Subject:


Attachment:


Later variants of the worm use different Subject fields and Attachment names.

The worm avoids sending e-mails to e-mail addresses that contain any of the following:



File infection

The worm scans all fixed and remote drives starting from Z: to C: and looks for files with the following extensions:


The worm collects additional e-mail addresses to spread to files with .hta, .txt and .htm extensions.

The files with .scr and .exe extensions get infected. For every executable file found, the worm creates a copy with a random name and a .t extension. Then it tries to infect the files, if they are in PE (Portable Executable) format. The worm inserts a small piece of code into the victim files and then redirects the entry point to that address. This small piece of code starts the worm's copy (randomly named file with .t extension) and then passes control to the host file. It should be noted that the worm is quite buggy and can corrupt files upon infection. The worm also does not infect files protected by Windows Safe File Check.

Files with .rar extension are not affected, but the worm's author probably plans to process them in future versions of his malware.


Payload

The worm terminates processes with the following substrings in their names:

In addition the worm closes the Registry Editor's window.

Last update 01 March 2007

 

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