Microsoft security software detects and removes this threat.

Win32/Magistr is a family of mass-mailing worms that spread by sending themselves as an email attachment to addresses found on an infected PC.

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

Use the following free Microsoft software to detect and remove this threat:

You should also run a full scan. A full scan might find hidden malware.

Get more help

You can also visit our advanced troubleshooting page or search the Microsoft virus and malware community for more help.

If you’re using Windows XP, see our Windows XP end of support page.

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.


Alerts from your security software might be the only symptom.


Alert level: Severe
This entry was first published on: Aug 16, 2011
This entry was updated on: Jul 16, 2015

This threat is also detected as:
No known aliases