Alert level

SettingsModifier:Win32/PossibleHostsFileHijack


Encyclopedia entry
Updated: Apr 16, 2009  |  Published: Dec 05, 2007

Aliases
  • Trojan.Win32.Qhost (Kaspersky)
  • Qhosts.apd (McAfee)

Alert Level (?)
Moderate

Antimalware protection details
Microsoft recommends that you download the latest definitions to get protected.
Detection last updated:
Definition: 1.69.200.0
Released: Oct 27, 2009 		Detection initially created:
Definition: 1.45.287.0
Released: Oct 07, 2008

Summary

A detection of Win32/PossibleHostsFileHijack is an indicator that your HOSTS file may have been modified by malicious or potentially unwanted software. Modifications to the HOSTS file can cause access to certain Internet domains to be redirected or denied. This may prevent the computer from connecting to certain Web sites.
 
To recover manually from Win32/PossibleHostsFileHijack, you can manually recreate a clean HOSTS file, or you can restore a version of the HOSTS file from a backup you made before the file was modified without your consent.
 
To recreate a clean HOSTS file:
  1. Click Start, and click Run.
  2. Open the Hosts file, according to operating system:

    On Windows 95, Windows 98, or Windows ME systems:
    In the Open field, type: notepad %windir%\hosts

    On Windows NT-based operating systems, such as Windows 2000 or Windows XP:
    In the Open field, type: notepad<system folder>\drivers\etc\hosts
    -- for example, on Windows 2000:
    In the Open field, type: notepad C:\WINNT\system32\drivers\etc\hosts
    -- or on Windows XP:
    In the Open field, type: notepad C:\Windows\system32\drivers\etc\hosts

    On Windows Vista:
    Click Start, click All Programs, click Accessories, right-click Notepad, and then click Run as administrator
    Click File, click Open, type: %windir%\system32\drivers\etc\hosts, and then click Open
  3. On the first line of the HOSTS file, type: 127.0.0.1 localhost as in the following example after modifying a default 'hosts' file:


  4. Save the file to the same location you opened it from.
  5. Close Notepad.

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Symptoms

Situations such as the following may be signs that your HOSTS file has been modified without your consent:
  • You are unable to access a certain Web site that you believe is in operation, such as a site that provides programs to help keep your computer secure.
  • Your browser connects to a Web site that does not appear to be appropriate, given the Web address you entered.

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Technical Information (Analysis)

Win32/PossibleHostsFileHijack indicates that the HOSTS file may have been modified by malicious or potentially unwanted software. The HOSTS file is located in <system folder>\drivers\etc\hosts, or in the Windows folder, depending on the Windows operating system being used.
 
The local HOSTS file overrides the DNS resolution of web site URL to IP address. Malicious software may make modifications to the HOSTS file to bypass DNS servers and resolve the URL to a different IP address. This may prevent your computer from accessing certain Web sites, such as sites that provide programs to help keep your computer secure.

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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 or are 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.

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Recovery

To recover manually from Win32/PossibleHostsFileHijack, you can manually recreate a clean HOSTS file, or you can restore a version of the HOSTS file from a backup you made before the file was modified without your consent.
 
To recreate a clean HOSTS file:
  1. Click Start, and click Run.
  2. Open the Hosts file, according to operating system:

    On Windows 95, Windows 98, or Windows ME systems:
    In the Open field, type: notepad %windir%\hosts

    On Windows NT-based operating systems, such as Windows 2000 or Windows XP:
    In the Open field, type: notepad<system folder>\drivers\etc\hosts
    -- for example, on Windows 2000:
    In the Open field, type: notepad C:\WINNT\system32\drivers\etc\hosts
    -- or on Windows XP:
    In the Open field, type: notepad C:\Windows\system32\drivers\etc\hosts

    On Windows Vista:
    Click Start, click All Programs, click Accessories, right-click Notepad, and then click Run as administrator
    Click File, click Open, type: %windir%\system32\drivers\etc\hosts, and then click Open
  3. On the first line of the HOSTS file, type: 127.0.0.1 localhost as in the following example after modifying a default 'hosts' file:


  4. Save the file to the same location you opened it from.
  5. Close Notepad.

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