Malicious Software Encyclopedia: Win32/Purstiu

Published: September 8, 2005

Win32/Purstiu is a family of Trojan downloaders that targets certain versions of Microsoft Windows. These Trojan downloaders are Internet Explorer browser helper objects (BHOs) that can download and run a file from a Web site.

Severity

What the levels mean

Glossary Terms

Click the term to get the definition from our Security Glossary.

•	Trojan horse
•	virus
•	worm

Threat Overview

Class/type	Trojan - Downloader
Discovered	June 14, 2005
Circulating	Yes
Affected operating systems	Windows 2000 Windows XP Windows Server 2003
Affected software	Not specified
Infection rating	Low
Recovery difficulty	Moderate
Damage rating	Medium
Transmission rating	Low

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Aliases (Also Known As)

Different antivirus vendors may be using different names to refer to this malicious software. Here are some of the names currently in use by antivirus software vendors participating in the Microsoft Virus Information Alliance (VIA):

McAfee: Downloader-ABZ trojan

Learn more about the Microsoft Virus Information Alliance.

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Technical Analysis

Win32/Purstiu is an Internet Explorer browser helper object (BHO). When it runs, it can download and run a file from a Web site. This can cause Windows Explorer (explorer.exe) to crash, which causes a dialog box to display, stating that such an error has occurred. A second dialog box, for the Dr. Watson program debugger, appears to ask whether you would like to send the error information to Microsoft. The Windows desktop (including the taskbar, Start button, and desktop icons) may disappear and then reappear.

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How to Prevent Infection

Take the following steps to help prevent infection on your system:

Enable a firewall on your computer.
Get the latest computer updates.
Use up-to-date antivirus software.

Enable a firewall on your computer

Use a third-party firewall product or turn on the Microsoft Windows XP Internet Connection Firewall.
To turn on the Internet Connection Firewall in Windows XP

Click Start, and click Control Panel.
Click Network and Internet Connections, and click Network Connections. If you do not see Network and Internet Connections, click Switch to Category View.
Highlight a connection that you want to help protect, and click Change settings of this connection.
Click Advanced, and select Protect my computer and network by limiting or preventing access to this computer from the Internet.
Click OK.

Get the latest computer updates

Updates help protect your computer from viruses, worms, and other threats as they are discovered. You can use the Automatic Updates feature in Microsoft Windows XP to automatically download future Microsoft security updates while your computer is on and connected to the Internet.
To turn on Automatic Updates in Windows XP

Click Start, and click Control Panel.
Click Performance and Maintenance. If you do not see Performance and Maintenance, click Switch to Category View.
Click System.
Click Automatic Updates, and select Keep my computer up to date.
Select a setting. Microsoft recommends selecting Automatically download the updates, and install them on the schedule that I specify and setting a regular update time.
If you choose to have Automatic Updates notify you in step 5, you will see a notification balloon when new downloads are available to install. Click the notification balloon to review and install updates.

Use up-to-date antivirus software

Most antivirus software can detect and prevent infection by known malicious software. You should always run antivirus software on your computer that is updated with the latest signature files to automatically help protect you from infection. If you don't have antivirus software installed, you can get it from one of several companies. For more information, see http://www.microsoft.com/athome/security/downloads/default.mspx

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How to Tell If Your Computer Is Infected

Win32/Purstiu can download a file from a Web site to your computer and run the file. This can cause Windows Explorer (explorer.exe) to crash, which causes a dialog box to display, stating that such an error has occurred. A second dialog box, for the Dr. Watson program debugger, appears to ask whether you would like to send the error information to Microsoft. The Windows desktop (including the taskbar, Start button, and desktop icons) may disappear and then reappear.

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