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Windows Defender Crash
Sunday, March 25, 2007
(The following applies to Windows XP only. Vista already has the newer version of Defender included.)

Windows Defender is in general a very nice and useful program, and I recommend it highly for most Windows users. It has had one recent problem:

The problem

Users started complaining about a problem with Windows Defender about 2 months ago. It seems that whenever they would log-in, an error dialog box with the following text appeared on the desktop:

Application failed to initialize: 0x800106ba. A problem caused this program's service to stop. To start the service, restart your computer or search Help and Support for how to start a service manually.

Restarting the computer simply repeated the error message, and searching "Help and Support" was no help. Luckiliy, the user could simply close the dialog and continue using the system with no apparent ill-effects, but minus Windows Defender.

Initially, I thought the problem was caused by a faulty update from Microsoft, but the reason is a bit different.

The solution

It turns out the old version of Windows Defender expired on Dec. 31, 2006, so starting Jan. 1, 2007 you'd get the above unhelpful error whenever Windows Defender tried to start (Thanks, Microsoft!).

The solution is to replace the old version of Windows Defender with the new one.

  • First, uninstall the old version of Defender as follows:
    • Start -> Control Panel -> Add/Remove Programs
    • Scroll down to "Windows Defender", click on it, then click on Remove
  • Download the new Windows Defender from:
    (Click the "Get it Now" button on that page)
  • Save the downloaded .msi file to any folder and run it by double-clicking on it.
  • The install is fairly straightforward, and the default options should be chosen.
    There is one decision you have to make early on:

    I recommend you "check" the middle box (Install definition updates only)
  • Choose default options the rest of the way. After the install, the following dialog appears:

    Leave the box "checked" and click "Finish"
    This is important, because it allows Defender to update with the latest def files.
  • The program will update and do a quick scan (takes 5 to 10 mins)
  • When it is done, close the dialog by using the X in the upper-right corner, and you are done.

The Defender error on startup should be gone.

In addition to Defender, you should also have one (and only one) anti-virus program installed on your PC.

Note that new version of Windows Defender requires Windows XP SP2 or later (it no longer runs on Win/2000 or XP/SP1). Defender is included by default in Vista and does not need to be installed separately.

Once Defender is installed, and you have Automatic Windows updates enabled (which you should), you will receive periodic update notifications in the system tray (about once a week). Do install the updates when the pop-up message in the system tray informs you.

By default, Windows Defender configures itself to scan your hard drive for malware every morning at 2 AM. If you want to change this time, or disable the auto-scan, open the Windows Defender program (from Start -> All Programs), click Tools -> Settings -> Options etc.

Some of the above is documented at

(in order from older to newest)

"I'm getting this problem now (4th May 2008) and have been for a few days. I'm about to reinstall the program after removing it from within Add/Remove Programs. I hope it works."

May 4, 2008, 5:51 AM by Mark.

"Well I removed the program using the add/remove programs thing and reinstalled a freshly downloaded copy of windows defender, unfortunately it didnt fix the issue and although it performed a quick scan correctly and said there were no issues it couldnt get through a complete scan without giving me the same error message as above, ie... Application failed to initialize: 0x800106ba. A problem caused this program's service to stop. To start the service, restart your computer or search Help and Support for how to start a service manually.

This is happening after a couple of minutes scanning the C Drive and before moving on to the other drives."

May 4, 2008, 6:08 AM by Mark.

"You might want to try the steps outlined in the following article from Microsoft:

specifically, the last two suggestions, i.e. (a) Uninstall Windows Defender and run the Windows Installer Cleanup Utility (see and (b) Re-register the DLL's listed step (3) of the Microsoft article 931849. "

May 5, 2008, 11:50 PM by rk.

"WOW! THANK YOU for making this EASY to follow! I'm not a puter geek, but def a puter addict! I did this all by myself! wooohooo...THANKS, again, for making it easy! =)."

July 26, 2008, 1:37 AM by Selva S.

"I attempted your fix but received this error when clicking on Windows Defender...'Application failed to initialize 0X800106ba. A problem caused this program's service to stop. To start this service, restart your computer. Search help & support to start a service manually'.

With each error I try to correct, I get yet another error. I am far from knowledgeable re computers, please help...layman's language please!! Thanks so much!

BTW, would this problem cause me to have no access to gmail or hotmail. All I get is 'This page cannot be displayed'.

My computer (Vista Home Premium) is a mess."

July 31, 2008, 6:07 PM by PP.

"Big problems with this error "Application failed to initialize: 0x800106ba"

It's not listed in add/remove programs and when I try download it, I get this message "windows defender is already installed on your vista" So what to do. I try all the help and solutions on the entire net."

Feb. 4, 2009, 2:38 AM by John T.

"I'm now getting this with Vista Home Premium and you can't uninstall Defender from Vista (Microsoft makes clear this fix is only for XP). Problem occurred with SP2 - rolling back to pre SP2 removes the problem, reinstalling it brings it back. Checking the DLLs as suggested by Microsoft for XP shows: wuaueng.dll and wintrust.dll loaded but call to DllregisterServer failed 0x8007005. wucltui.dll, wuweb.dll and initpki.dll all failed to load. I'm out of knowledge / ideas - help much appreciated!!"

May 31, 2009, 5:50 AM by DW

"started my laptop and a security center alert popped up and some program called malware from guardsoft starts running automatically trying to install , since this has happened i cannot access the internet and more security aletrs keep popping up tried to scan the pc and the antivirus (norton) program i use freezes up every time i try to run windows defender and i get an error message stating the the defender interface has stopped working tried a system restore and i get an error message stating that the process could not be completed due to the process being interrupted or an error message saying catastrophic failure please help"

Jan. 9, 2010, 10:34 AM by RR

"Not sure how much I can help, but here is what I suggest:

(1) Using another computer, download Combofix from:

(instructions are at:

(2) Put the combofix.exe file on a memory stick.

(3) Boot the infected laptop in "Safe Mode" (tap the F8 key when first starting up and select Safe Mode from the menu)

(4) Copy Combofix.exe from the memory stick to the infected laptop

(5) Run Combofix by double-clicking on it. It may take 30 or more minutes, let it finish.

You may have to repeat running Combofix once or twice.

(6) If the machine then lets you boot in normal mode, run Combofix again."

Jan. 9, 2010, 10:46 AM by rk

"just wanted to say thank you so much for the information you provided . and thank you for directing me to bleepingcomputer . between your info and the info on that site i was able to get the malware off my laptop . i can't tell you how much i appreciate that , again , thank you."

Jan. 9, 2010, 7:34 PM by RR

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(This page last modified on Mar. 19, 2010)

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