If you use more than one antivirus or antispyware program at the same time, your computer may experience decreased performance, become unstable, or restart unexpectedly. Before you install Microsoft Security Essentials, or to resolve many issues with Security Essentials, including installation issues, you must first completely remove any Internet security programs from your computer as described in this topic.

Caution:
When you remove your currently installed Internet security programs, your computer is in an unprotected state. If you have problems installing Microsoft Security Essentials after you remove your existing Internet security programs, contact Microsoft Security Essentials Support by submitting a case online.
Tip:
You will need to restart your computer while following these instructions. Write them down, print them, or bookmark this page (mark it as a Favorite) to make it easier to find this topic again.

Step 1: Remove antivirus or antispyware programs

  1. In Windows XP, click Start, click Run, type appwiz.cpl, and then press Enter.

    -or-

    In Windows Vista, click Start. In the Start Search box, type appwiz.cpl, and then press Enter.

    –or–

    In Windows 7, click Start. In the Search programs and files box, type appwiz.cpl, and then press Enter.

  2. In the list of installed programs, uninstall any other Internet security programs.

  3. Restart your computer.

Note:
  • Some Internet security applications do not uninstall completely. You may need to download and run a cleanup utility for your previous security application for it to be completely removed.

  • If you use another antispyware program together with Microsoft Security Essentials, we recommend that you turn off real-time scanning in the other program. For more information, see the documentation supplied by that antispyware program.
Important:
If your antivirus program is disabled or if you do not have one installed, you should follow these guidelines:
  • Do not download or open files from sources that you do not trust.

  • Do not visit Web sites that you do not trust.

  • Do not open e-mail attachments from contacts that you do not trust.

Step 2: Completely uninstall Windows Live OneCare

  1. Microsoft Windows Live® OneCare does not always uninstall completely. If you have recently uninstalled Windows Live OneCare, you should download the Windows Live OneCare Utility cleanup tool by clicking http://go.microsoft.com/fwlink/?LinkId=167350.

  2. In Microsoft Windows Internet Explorer®, in the File Download – Security Warning dialog box, click Save. Browse to the location where you want to save the file, and then click Save.

  3. Navigate to the location where you saved the file.

  4. In Windows XP, double-click the file.

    -or-

    In Windows Vista, right-click the file, and then click Run as administrator.

  5. Click Run, and then click Continue.

  6. Read the licensing agreement. If you agree, select I accept the terms of the End User Licensing Agreement, and then click Continue.

  7. Click Clean.

  8. After the clean-up tool finishes, click Restart Now.