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Win32/Zotob


Win32/Zotob is a network worm that primarily targets Microsoft Windows 2000 computers that do not have Microsoft Security Bulletin MS05-039 installed. MS05-039 patches the Windows Plug-and-Play buffer overflow vulnerability. Win32/Zotob can also infect computers running other Windows operating systems if it is delivered through e-mail, instant messaging, or other routes. The worm has a backdoor component that connects to an IRC server to receive commands from attackers.


What to do now

Manual removal is not recommended for this threat. To detect and remove this threat and other malicious software that may have been installed, run a full-system scan with an up-to-date antivirus product such as the Microsoft Safety Scanner (http://go.microsoft.com/fwlink/?LinkId=212742). For more information, see http://www.microsoft.com/protect/computer/viruses/vista.mspx.

Threat behavior

Win32/Zotob takes the following actions:
  • Copies itself to the Windows system folder.
  • Exits after running the copied worm file. The worm copy then takes the following actions:
    • Modifies the Windows registry so that the worm copy runs each time Windows starts.
    • Scans random IP addresses to establish connections with other computers. The worm sends exploit code to a remote computer when a connection is established. If the remote computer is running Windows 2000 and does not have MS05-039 installed, the exploit code causes the remote computer to download and run a copy of the worm.
    • Connects to an IRC server to receive commands such as the following from attackers:
      • Retrieve system information such as CPU speed, memory usage, Windows operating system, connection type, IP address, and Windows logon information.
      • Download and run files.
      • Remove the worm.
    • Modifies the Windows system hosts file, <system folder>\drivers\etc\hosts, to block access to certain Web sites.
    • Disables the Internet Connection Firewall/Internet Connection Sharing service by modifying a registry key.
 
Certain Win32/Zotob variants can also perform actions such as the following:
  • Terminate other processes and delete certain files in the Windows system folder or Windows program files folder.
  • Register the worm as a service. This causes the worm to start as a service each time Windows starts, so that the worm continues running regardless of whether any user is logged on. 
  • Monitor a specific port for requests. Upon receiving a request, the worm can send a copy of itself to another computer using a protocol such as TFTP.
  • Spread through e-mail by sending a copy of the worm as an attachment to e-mail addresses found on the infected computer.
  • Remove or disable certain adware, spyware, and malicious software applications.

Symptoms

There are no readily apparent indications that your computer is infected with a variant of Win32/Zotob. However, certain symptoms may indicate that your computer is infected by this worm. See the Win32/Zotob child variants for more information.

Prevention

Take the following steps to help prevent infection on your system:
  • Enable a firewall on your computer.
  • Get the latest computer updates for all your installed software.
  • Use up-to-date antivirus software.
  • Use caution when opening attachments and accepting file transfers.
  • Use caution when clicking on links to web pages.
  • Avoid downloading pirated software.
  • Protect yourself against social engineering attacks.
  • Use strong passwords.
Enable a firewall on your computer
Use a third-party firewall product or turn on the Microsoft Windows Internet Connection Firewall.
To turn on the Windows Firewall in Windows Vista
  1. Click Start, and click Control Panel.
  2. Click Security.
  3. Click Turn Windows Firewall on or off.
  4. Select On.
  5. Click OK.
To turn on the Internet Connection Firewall in Windows XP
  1. Click Start, and click Control Panel.
  2. Click Network and Internet Connections. If you do not see Network and Internet Connections, click Switch to Category View.
  3. Click Change Windows Firewall Settings.
  4. Select On.
  5. Click OK.
Get the latest computer updates
Updates help protect your computer from viruses, worms, and other threats as they are discovered. It is important to install updates for all the software that is installed in your computer. These are usually available from vendor websites.
 
You can use the Automatic Updates feature in Windows to automatically download future Microsoft security updates while your computer is on and connected to the Internet.
To turn on Automatic Updates in Windows Vista
  1. Click Start, and click Control Panel
  2. Click System and Maintainance.
  3. Click Windows Updates.
  4. Select a setting. Microsoft recommends selecting Install updates automatically and choose a time that is convenient for you. If you do not choose Automatic, but you choose to be notified when updates are ready, a notification balloon appears when new downloads are available to install. Click the notification balloon to review and install the updates.
To turn on Automatic Updates in Windows XP
  1. Click Start, and click Control Panel
  2. Click System.
  3. Click Automatic Updates.
  4. Select a setting. Microsoft recommends selecting Automatic. If you do not choose Automatic, but you choose to be notified when updates are ready, a notification balloon appears when new downloads are available to install. Click the notification balloon to review and install the updates.
Use up-to-date antivirus software
Most antivirus software can detect and prevent infection by known malicious software. To help protect you from infection, you should always run antivirus software that is updated with the latest signature files. Antivirus software is available from several sources. For more information, see http://www.microsoft.com/protect/computer/viruses/vista.mspx.
Use caution when opening attachments and accepting file transfers
Exercise caution with e-mail and attachments received from unknown sources, or received unexpectedly from known sources.  Use extreme caution when accepting file transfers from known or unknown sources.
Use caution when clicking on links to Web pages
Exercise caution with links to web pages that you receive from unknown sources, especially if the links are to a Web page that you are not familiar with, unsure of the destination of, or suspicious of. Malicious software may be installed in your system simply by visiting a Web page with harmful content.
Avoid downloading pirated software
Threats may also be bundled with software and files that are available for download on various torrent sites. Downloading "cracked" or "pirated" software from these sites carries not only the risk of being infected with malware, but is also illegal. For more information, see 'The risks of obtaining and using pirated software'.
Protect yourself from social engineering attacks
While attackers may attempt to exploit vulnerabilities in hardware or software in order to compromise a system, they also attempt to exploit vulnerabilities in human behavior in order to do the same. When an attacker attempts to take advantage of human behavior in order to persuade the affected user to perform an action of the attacker's choice, it is known as 'social engineering'. Essentially, social engineering is an attack against the human interface of the targeted system. For more information, see 'What is social engineering?'.
Use Strong Passwords
Attackers may try to gain access to your Windows account by guessing your password. It is therefore important that you use a strong password – one that cannot be easily guessed by an attacker. A strong password is one that has at least 8 characters, and combines letters, numbers, and symbols. For more information, see http://www.microsoft.com/protect/yourself/password/create.mspx.

Alert level: Severe
This entry was first published on: Aug 17, 2005
This entry was updated on: Apr 17, 2011

This threat is also detected as:
  • W32/Zotob.worm (McAfee)
  • W32/Zotob.worm.gen (McAfee)
  • W32.Zotob (Symantec)
  • W32/Bozor.A.worm (Panda)
  • WORM_MYTOB.JS (Trend Micro)
  • W32/Zotob-A (Sophos)
  • Zotob.A (F-secure)
  • Win32/Zotob.A!Worm (CA)
  • Net-Worm.Win32.Mytob.cd (Kaspersky)