W32/Mytob-AR

Please follow the instructions for removing worms.

Replace the Hosts file from a backup or edit it in Notepad to remove the changes that the worm has made.

You will also need to edit the following registry entries, if they are present. Please read the warning about editing the registry.

At the taskbar, click Start|Run. Type 'Regedit' and press Return. The registry editor opens.

Before you edit the registry, you should make a backup. On the 'Registry' menu, click 'Export Registry File'. In the 'Export range' panel, click 'All', then save your registry as Backup.

Locate the HKEY_LOCAL_MACHINE entries:

HKLM\Software\Microsoft\Windows\CurrentVersion\Run

HKLM\Software\Microsoft\Windows\CurrentVersion\RunServices

and remove any reference to any file you deleted.

Each user has a registry area named HKEY_USERS\[code number indicating user]\. For each user locate the entry:

HKU\[code number]\Software\Microsoft\Windows\
CurrentVersion\Run\

and remove any reference to any file you deleted.

Close the registry editor.

W32/Mytob-AR is a mass-mailing worm and IRC backdoor Trojan for the Windows platform.

W32/Mytob-AR spreads to other network computers by exploiting common buffer overflow vulnerabilites, including LSASS (MS04-011) and by copying itself to network shares protected by weak passwords.

W32/Mytob-AR runs continuously in the background, providing a backdoor server which allows a remote intruder to gain access and control over the computer via IRC channels.

When first run W32/Mytob-AR copies itself to the Windows system folder as msvhost.exe and creates the following registry entries:

HKLM\Software\Microsoft\Windows\CurrentVersion\RunServices
WINTASK
msvhost.exe

HKLM\Software\Microsoft\Windows\CurrentVersion\Run
WINTASK
msvhost.exe

HKCU\Software\Microsoft\Windows\CurrentVersion\Run
WINTASK
msvhost.exe

HKLM\SYSTEM\CurrentControlSet\Control\Lsa
WINTASK
msvhost.exe

HKCU\SYSTEM\CurrentControlSet\Control\Lsa
WINTASK
msvhost.exe

HKLM\SOFTWARE\Microsoft\Ole
WINTASK
msvhost.exe

HKCU\Software\Microsoft\Ole
WINTASK
msvhost.exe

W32/Mytob-AR copies itself to the root folder as:

funny_pic.scr
my_photo2005.scr
see_this!!.scr

and drops a file called hellmsn.exe (detected by Sophos as W32/Mytob-D) in the same location. This component attempts to spread the worm by sending files through Windows Messenger to all online contacts.

W32/Mytob-AR also includes functionality to silently download, install and run new software as well as terminate anti-virus and security related applications.

W32/Mytob-AR modifies the HOSTS file, changing the URL-to-IP mappings for selected websites, therefore preventing normal access to these sites. The new HOSTS file will typically contain the following:

127.0.0.1 www.symantec.com
127.0.0.1 securityresponse.symantec.com
127.0.0.1 symantec.com
127.0.0.1 www.sophos.com
127.0.0.1 sophos.com
127.0.0.1 www.mcafee.com
127.0.0.1 mcafee.com
127.0.0.1 liveupdate.symantecliveupdate.com
127.0.0.1 www.viruslist.com
127.0.0.1 viruslist.com
127.0.0.1 viruslist.com
127.0.0.1 f-secure.com
127.0.0.1 www.f-secure.com
127.0.0.1 kaspersky.com
127.0.0.1 www.avp.com
127.0.0.1 www.kaspersky.com
127.0.0.1 avp.com
127.0.0.1 www.networkassociates.com
127.0.0.1 networkassociates.com
127.0.0.1 www.ca.com
127.0.0.1 ca.com
127.0.0.1 mast.mcafee.com
127.0.0.1 my-etrust.com
127.0.0.1 www.my-etrust.com
127.0.0.1 download.mcafee.com
127.0.0.1 dispatch.mcafee.com
127.0.0.1 secure.nai.com
127.0.0.1 nai.com
127.0.0.1 www.nai.com
127.0.0.1 update.symantec.com
127.0.0.1 updates.symantec.com
127.0.0.1 us.mcafee.com
127.0.0.1 liveupdate.symantec.com
127.0.0.1 customer.symantec.com
127.0.0.1 rads.mcafee.com
127.0.0.1 trendmicro.com
127.0.0.1 www.microsoft.com
127.0.0.1 www.trendmicro.com

W32/Mytob-AR is capable of spreading through email. Email sent by W32/Mytob-AR has the following properties:

Subject line:

Good day
hello
Mail Delivery System
Mail Transaction Failed
Server Report
Status
Error

Message text:

'Mail transaction failed. Partial message is available.'
'The message contains Unicode characters and has been sent as a binary attachment.'
'The message cannot be represented in 7-bit ASCII encoding and has been sent as a binary attachment.'
'The original message was included as an attachment.'
'Here are your banks documents.'
<random characters>

The attached file consists of a base name followed by the extentions PIF, SCR, EXE or ZIP. The worm may optionally create double extensions where the first extension is DOC, TXT or HTM and the final extension is PIF, SCR, EXE or ZIP.

W32/Mytob-AR harvests email addresses from files on the infected computer and from the Windows address book.

The following patch for the operating system vulnerability exploited by W32/Mytob-AR can be obtained from the Microsoft website:

(MS04-011)

Sophos's anti-virus products include Genotype ™ detection technology, which can proactively protect against new threats without requiring an update. Sophos customers have been protected against W32/Mytob-AR (detected as W32/Mytob-Fam) since version 3.92.