I have been having this problem with windows defender for a very long time. Whenever I click the update definitions on Windows Defender I get an error code and it is unable to update. My AVG antivirus and Comodo firewall have no problems updating. Even my windows update works properly. I tried disabling all firewalls but it is still the same problem.

If I cant solve this...how do I uninstall windows defender? I hate getting the pop up about outdated definitions file on startup...

Hi

Close Windows Defender from system tray, Right click the little icon next to the clock and select Exit.

If you delete the old update, checking for new updates will work.

To do this, Press Start > Run and type Msiexec /x {A5CC2A09-E9D3-49EC-923D-03874BBD4C2C} and click OK (you can copy and paste the Msiexec bit).

Open Windows Defender and check for updates.

If the above fails, try the following:

Windows XP and Windows Server 2003

1. Click Start, click Run, type wuaucpl.cpl, and then click OK.
2. Click Automatic (Recommended), and then click OK.

Windows Vista

1. Click the Start Orb, click All Programs, and then click Windows Update.
2. In the left pane, click Change settings.
3. Click to select Install updates automatically (recommended).
4. Under Recommended updates, select the Include recommended updates when downloading, installing, or notifying me about updates check box, and then click OK.

User Access Control - If you are prompted for an administrator password or for confirmation, type the password, or provide confirmation.

hmm....first few methods didnt work...
i tried install updates automatically but i got an error code too

oh yea...for the MSIEXEC bit i got an error saying this action is only available for products currently installed...

Try the update procedure on this link.

thanks! it works!

HI, just joined this site out of desparation. Suddenly Windows Defender is asking me for a password before I can access my e-mail account using Windows Mail (never did it before) but worse - when I complete it I am informed I have no new mail. But if I check mail2web.com, lo and behold I have mail waiting for me! Any clues as to what's going on? Defender will not allow me to update saying it does not recognise my processor (Intel Pentium dual core) I can't seem to disable Windows Defender as it tells me it's not running yet still keeps flashing up a password request.

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