Win32/Zlob is a family of Trojans that modify Internet Explorer settings, redirect the default internet search and home pages, and attempt to download and execute malicious software from the Internet.

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 Microsoft Security Essentials, or the Microsoft Safety Scanner. For more information about using antivirus software, see

Threat behavior

When variants of the Win32/Zlob trojans are executed, they may perform the following actions:
  • Drop a copy of themselves on the computer, in locations such as:
  • <program files>\messenger\msmsgs.exe
    <system folder>\tgbrfv_.exe
    <system folder>\cmd.exe
  • Configure the dropped copy as an auto start program and safeboot service, such as:
  • Set "notepad.exe" = "<dropped copy>", under key HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\policies\explorer\run
    Set "Start" = "2", under key HKLM\SYSTEM\CurrentControlSet\Services\pnpsvc
    Set "EventMessageFile" = "<dropped copy>", under key HKLM\SYSTEM\CurrentControlSet\Services\EventLog\Application\pnpsvc
    Set "(default)" = "service", under key HKLM\SYSTEM\CurrentControlSet\Control\SafeBoot\Minimal\pnpsvc
  • Inject remote threads in other processes, such as:
  • winlogon.exe
  • Connect to remote Web servers at TCP port 80, such as:
  • Reconfigure the Internet Explorer start or default search page
  • Modify the HOSTS file to redirect attempts to access certain Web sites


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.
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 Web sites.
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.
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, such as Microsoft Security Essentials, that is updated with the latest signature files. For more information, see
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

Alert level: High
This entry was first published on: Apr 21, 2007
This entry was updated on: Apr 17, 2011

This threat is also detected as:
  • Win32/Zlob (CA)
  • TROJ_ZLOB (Trend Micro)