Win32/Magistr is a family of mass-mailing worms that spread by sending themselves as an e-mail attachment to addresses found on an infected computer. It is also a memory resident polymorphic file infector that searches and infects files with .EXE and .SCR file extensions found on the local file system, as well as in the shared folders on the local area network.

What to do now

To detect and remove this threat and other malicious software that may be installed on your computer, run a full-system scan with an appropriate, up-to-date, security solution. The following Microsoft products detect and remove this threat:

For more information on antivirus software, see

Threat behavior

When Win32/Magistr runs, it injects a 110 bytes viral routine into the process space of Explorer to remain memory resident. After sleeping for a few minutes, the viral routine starts the mass-mailing action. It collects e-mail addresses from Windows Address Books, Outlook Express Address Books and Netscape Messenger mail files. Some variants of the worm also search Eudora address books for e-mail address. The worm saves the addresses to a .DAT file in Widows folder or Program Files folder, or under the root folder. The .DAT file also stores the date information of the worm's initial execution. The worm then sends e-mails to those e-mail addresses found on the infection computer. The e-mail messages may include infected executable attachment with .EXE, .SCR or .PIF file extension. The sender e-mail address is spoofed. The subject line, message body text and attachment name may vary. The message body and subject line often include random words and phrases taken from .doc and .txt files on the infection computer.

In order to run each time Windows starts, Win32/Magistr also adds a registry value pointing to an infected file under the registry key HKLM\Software\Microsoft\Windows\CurrentVersion\Run.

Some variants of the Win32/Magistr also add an execution instruction of "run =<infected file>" into the "[Windows]" section of the Windows configuration file "win.ini". Alternatively, the Magistr can add another execution instruction of "shell=explorer.exe <infected file>" into the "[Boot]" section of the Windows configuration file "system.ini" to achieve similar results.

The worm is also a file infector. It infects files with .EXE and .SCR file extensions in Widows folder. It also searches and infects on local hard drives, mapped network drives, as well as the shared folders on the local area network which it has write access. Upon infection, the virus appends its encrypted viral body to the last section of the infected file, modifies the host file with some polymorphic tricks to avoid being detected and passes the control to the virus own routine when the infected file runs.

Under certain conditions, Win32/Magistr triggers its destructive payloads. Those conditions may be the amount of time after its initial execution, or the infection counter reaches a certain number.

The payloads may include:

  • Overwriting files
  • Deleting files on local system and shared network resources
  • Disable security-related products
  • Producing a visual effect that the desktop icons look like "running away" when mouse cursor approaches them
  • On a computer running Windows 9x or Windows ME, it may destroy hard disk data, erase CMOS data and Flash BIOS setting. 

Win32/Magistr is polymorphically encrypted and uses anti-debugging tricks to make it more difficult to analyze and detect.


Take the following steps to help prevent infection on your computer:
  • Enable a firewall on your computer.
  • Get the latest computer updates for all your installed software.
  • Use up-to-date antivirus software.
  • Limit user privileges on the computer.
  • Use caution when opening attachments and accepting file transfers.
  • Use caution when clicking on links to webpages.
  • 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 websites. Instructions on how to download the latest versions of some common software is available from the following:

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

Limit user privileges on the computer

Starting with Windows Vista and Windows 7, Microsoft introduced User Account Control (UAC), which, when enabled, allowed users to run with least user privileges. This scenario limits the possibility of attacks by malware and other threats that require administrative privileges to run.

You can configure UAC in your computer to meet your preferences:

Use caution when opening attachments and accepting file transfers

Exercise caution with email 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 webpages

Exercise caution with links to webpages that you receive from unknown sources, especially if the links are to a webpage that you are not familiar with, unsure of the destination of, or suspicious of. Malicious software may be installed in your computer simply by visiting a webpage 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 to compromise a computer, they also attempt to exploit vulnerabilities in human behavior to do the same. When an attacker attempts to take advantage of human behavior 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 computer. 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 eight characters, and combines letters, numbers, and symbols. For more information, see

Alert level: Severe
This entry was first published on: Aug 16, 2011
This entry was updated on: Aug 30, 2011

This threat is also detected as:
No known aliases