I can't start the Microsoft Security Essentials service

Symptom

You receive a message notifying you that “Microsoft Security Essentials isn't monitoring your computer because the program's service stopped. You should restart it now.

Solution

Step 1: Restart your computer

  • Close all apps and restart your computer.

Step 2: Make sure the “Microsoft Security Essentials” service is set to automatic and is started

  1. In Windows XP, click Start, click Run, type services.msc, and then press Enter.
    –or–
    In Windows Vista and Windows 7, click Start, click in the Start Search box, type services.msc, and then press Enter.

  2. Search for Microsoft Antimalware Service. Right-click it and select Properties or double-click it to open the service.

  3. Check to make sure that the "Startup Type" is set to "Automatic".

  4. Click the Start button to start the service. If the Start button isn't available, click the Stop button, and then click the Start button to restart the service.

  5. Make sure you note any errors that may appear during this process, submit a case online, and include the error information.

Step 3: Remove any existing Internet security programs

  1. In Windows XP, click Start, click Run, type appwiz.cpl, and then press Enter
    –or–
    In Windows Vista or Windows 7, click Start, click in the Start Search box, type appwiz.cpl, and then press Enter.

  2. In the list of installed programs, uninstall any third-party Internet security programs.*

  3. Restart your computer, and then try to install Microsoft Security Essentials again.

Note:

*Some Internet security apps don't uninstall completely. You may need to download and run a cleanup utility for your previous security app in order for it to be completely removed.

Caution:

When you remove Internet security programs, your computer is unprotected. If you have problems installing Microsoft Security Essentials after you remove existing Internet security programs, contact Microsoft Security Essentials Support immediately by submitting a case online (for more information, see Submit a support case).

Step 4: Uninstall/reinstall Microsoft Security Essentials

  1. In Windows XP, click Start, click Run, type appwiz.cpl, and then press Enter.
    -or-
    In Windows Vista and Windows 7, click Start, and in the Start Search box, type appwiz.cpl, and then press Enter.

  2. In the list of installed programs, click Microsoft Security Essentials, and then uninstall it.

  3. If prompted, restart your computer, and then try to install Microsoft Security Essentials again.