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Dealing with the Error: rundll32.exe is not a valid win32 application

April 4, 2009

in privacy & security,Windows

by David Hakala

Q: How do I fix the error: rundll32.exe is not a valid win32 application? — Ashok

This error message is a sure sign that your computer is infected with malware of some kind. Something has replaced the valid rundll32.exe file with an identically named file that does who knows what. Whatever did it is probably hiding somewhere else on your machine, waiting to do it again if you simply replace rundll32.exe with a clean copy from your Windows installation CD.

You can try various anti-malware programs such as Avast! Antivirus, Spybot, etc. But there is no guarantee that the hidden program will be found and eradicated. The only way to fully protect yourself against identity theft or having your computer exploited to distribute more malware is to wipe your hard drive clean and start all over from scratch.

First, disconnect this machine from the Internet. It may be transmitting your personal data to some bad guys right now, or passing infections to other Internet users.

Second, go to a known uninfected machine and change every user ID and password combination that you use to access bank accounts and other sensitive sites.

Do these things right now, before you even finish reading this article! You are in immediate danger of becoming a victim of fraud and theft.

Third, install an anti-malware program and run it on all of your user data, including everything in My Documents and its subfolders. Then copy all of your user data to CD, DVD, or some other offline storage media.

Fourth, do a clean installation of Windows. If your computer came with a “System Restore” CD or has a “System Restore” feature on its hard drive, run that to restore your computer to its factory condition. If you have a full retail copy of Windows on CD, insert that CD in the CD drive, restart your computer, and reformat your primary hard drive when given the opportunity to do.

Fifth, re-install all of your application programs from known clean sources: original CDs or freshly downloaded copies.

Sixth, replace all of your user data in newly created subfolders.

Seventh, install anti-malware software that continually monitors what’s written to your hard drive to prevent future infections.

David Hakala has perpetrated technology tutorials since 1988 in addition to committing tech journalism, documentation, Web sites, marketing collateral, and profitable prose in general. His complete rap sheet can be seen at

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