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I use Microsoft Security Essentials as my antivirus on my Win7 box. New virus definitions to Security Essentials are installed using Windows Update. However, the updates are marked as optional by default, as opposed to important which means that they don't get installed automatically. I have to select the updates from the list of optional updates and install them manually.

Is there a way to change this behavior so that new definitions are marked as important and installed automatically?

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up vote 4 down vote accepted

Do you have MSE set to run Scheduled scan? You can force MSE to check for updates before a scheduled scan. To set a scheduled scan open up MSE and click on the settings tab. Check the box "Run a scheduled scan" and set the day, time, and type of scan. Then make sure you check the box for "Check for the latest virus & spyware definitions before running a scheduled scan".

Updated 01/14/2011

Here is a link to a way to change the frequency of MSE updates. The default is every 24 hours.

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+1 for Scheduled Scan. Additionally you can go to the update tab and manually update SCE. – Xavierjazz Oct 7 '10 at 4:43
Checking before a scheduled scan appears to be the default setting. – Velociraptors Oct 7 '10 at 4:48
Just read at Downloadsquad about a new screensaver that use MSE to scan your computer while it is idle during the day.… – RSMoser Oct 7 '10 at 15:18
Setting the MSE updates as required or important could make it seem that MSE is a required installation for Windows. This would then lead to some legal issues. See this article from Computer World.… – RSMoser Nov 7 '10 at 12:49

You can check for, download, and install new updates on the command line with the following command:


"%ProgramFiles%\Microsoft Security Essentials\MpCmdRun.exe" -SignatureUpdate


"%ProgramFiles%\Microsoft Security Client\Antimalware\MpCmdRun.exe" -SignatureUpdate
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Might be worth emphasising that it will also download and install those updates, rather than just checking if any are available. – Richard Oct 7 '10 at 12:58
Might be worth adding to this answer (I don't know if this is a permanent change) but on my Windows 7 machine it is under the following Program Files folder "Microsoft Security Client" – CodeBlend Jun 21 '13 at 7:40
BTW how did you find out such a useful piece of information? – CodeBlend Jun 21 '13 at 7:42

To the best of my knowledge, the files should be installed automatically anyway. Try leaving things alone for say, a month or so, and then take a peek at MSE's definition information.

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I think this is poor advice. Malware is moving so fast, a month may cause a real problem. -1. – Xavierjazz Oct 7 '10 at 5:16
The advice is spot-on. In the default MSE configuration, updates are auto-applied. If you leave it alone for a month, your updates will still be up-to-date. – afrazier Oct 7 '10 at 16:06


Q: Why are Definition updates for MSE considered OPTIONAL updates

A: They are marked optional in Windows Update because if they are ignored MSE will install the definitions at its regular daily update check

Therefore you will not need to set them to important as MSE installs them anyway.

Its quite a helpful site for all things MSE related.
Hope this clears up your query.

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