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Microsoft security software help

If you're using Windows XP, see our Windows XP end of support page.

You can find answers to common questions about Microsoft security software, including updates, where to download, and common software errors on this page.

If you can't find the answer you're looking for, see these other topics:

You can also visit the Microsoft virus and malware community for more help.

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Support for Windows XP ended on April 8, 2014.

Our Windows XP end of support page has links and information that explains what this means.

A quick scan will look for viruses and other malware in all the places they are most likely to hide. It’s a good choice when you’re just checking on the health of your PC.

If you think your PC is infected with malware, we recommend a full scan. Your PC might be a little slower while the full scan is running because it looks everywhere for possible problems.

First, make sure you've updated all of the apps on your PC. See our updating software help page for links to some common apps.

You should also install the latest definitions from our website. This will be more recent than those offered in your security software when you click Update.

If you are still having problems, you can ask for help at the Microsoft virus and malware community.

Partially removed means we were able to clean some of the malware files that we found on your PC.

We'll do our best to clean your PC as much as we can, but with some difficult malware you might need to take some additional steps:

  • Run a full scan using the Malicious Software Removal Tool:

    1. Open a Run prompt by pressing Windows Logo Key + R or typing Run in the Start screen or Start menu search bar.

    2. Type %windir%\system32\mrt.exe and press OK.

    3. If you are prompted to allow the program to make changes to your PC, click Yes.

    4. Follow the prompts to scan and clean your PC.

  • Restart your PC.

  • Manually install the latest updates.

  • Follow the steps on our advanced troubleshooting page for more help. In particular, you may need to use Windows Defender Offline.

We recommend that you do not run other antivirus or antispyware products at the same time as Microsoft Security Essentials or Windows Defender.

Using more than one real-time security product can affect your PC's performance. You might also get an error code when you try to update or install, such as 0x80070643.

Microsoft security software protects you against malware, spyware, adware, and other unwanted software; you don't need to install any other real-time antivirus or antispyware software.

If you install our software, you should:

You can always download and run our one-off security scanners, such as the Microsoft Safety Scanner or Windows Defender Offline. These scanners work at the same time as any real-time security software.

Before the release of Windows 8.1, Windows Defender referred to a separate tool that only detected spyware. This tool is no longer supported, as antispyware is included in Microsoft Security Essentials and Windows Defender.

No. You can’t use Microsoft Security Essentials and Windows Defender at the same time, but you don’t need to - they both protect your PC from malware and other threats in exactly the same way.

Windows Defender only works on Windows 8.1. Microsoft Security Essentials only works on Windows 7 and Windows Vista.

Windows Defender on Windows 7 and Windows Vista is a separate antispyware tool that is not needed if you already have Microsoft Security Essentials.

Windows Defender is built into Windows 8.1. If you’re using Windows 8.1, you don't need to download or install anything extra as you’re already protected.

If you’re using Windows 7 or Windows Vista, you can download Microsoft Security Essentials.

To disable Windows Defender:

  1. Open the Start screen.

  2. Type Windows Defender and click on the Windows Defender icon.

  3. Click the Settings tab.

  4. Under Administrator, clear the Turn on this app check box.

Windows Defender comes built into Windows 8.1. You can turn off Windows Defender if you decide to use a different security product.

Your PC will be vulnerable to malware if you disable Windows Defender and don’t have another security product.

If you don't have another security product, or it is expired, Windows Defender will automatically turn on.

You can also enable it manually (you can't do this if you already have a security product installed and working):

  1. Open the Start screen.

  2. Type Windows Defender and click on the Windows Defender icon.

  3. Click the Settings tab.

  4. Under Administrator, select the Turn on this app check box.

Generally, you don’t need to do anything as the security software will clean the infection for you.

If unwanted software has been found on your PC you may be asked to choose what to do next. When this happens you will see a message in the bottom corner of your screen, where you can choose to click Clean computer or Show details.

If you choose Clean computer the file is removed.

The Show details button lets you choose to either remove, quarantine, or allow the file.

Every threat is given an alert level to help you decide what to do.

This depends on how much you know about the file that has been detected.

  • Remove deletes the file from your PC.

  • Quarantine moves the file to a new location and blocks it so it can't run.

  • Allow adds the file to an allowed list and lets it run on your PC.

If you allow a file you won’t get any more alerts about it. Only allow a file if you trust the software and the software publisher.

A threat’s alert level can help you decide what to do.

  1. Open Microsoft Security Essentials or Windows Defender.

  2. Click the History tab.

  3. Select Quarantined items and then View details. You might be asked for an admin password or to confirm your choice.

Once you have reviewed the quarantined items you can either:

  • Select Remove all to delete all quarantined software.

  • Select individual files, and then click Remove or Restore.

Most files detected by Microsoft security software are quarantined. This means the file is moved and stopped from running or doing anything to your PC.

A quarantined file does not pose any risk to your PC. You can leave a file in quarantine for as long as you like.

Alert levels help you choose what to do when unwanted software is found on your PC.

Microsoft uses four alert levels:

  • Severe – widespread or highly dangerous malware that can affect your privacy and damage your PC.

  • High – programs that can collect your personal information or make changes to your PC.

  • Medium – programs that might affect your privacy or change the way your PC behaves.

  • Low - unwanted software that might collect information about you or your PC or change how your PC works.

Alert levels help you understand how dangerous a threat could be and decide what to do next.

Go to the Understanding alert levels page for more information.

To force a scan of a removable drive:

  1. Open File Explorer (Windows 8.1) or Windows Explorer (Windows 7 and Windows Vista).

  2. Rick-click the removable drive.

  3. Click Scan or Scan with Your security software's name.

To always scan removable drives when you do a full scan:

  1. Open your Microsoft security software.

  2. Go to the Settings tab.

  3. In the Advanced section, select the Scan removable drives check box.

  4. Click Save changes. Whenever you do a full scan, all removable drives will also be scanned.

You can choose to exclude files from scanning if you know they are completely safe.

You should only do this for files you know are absolutely clean - if you are getting repeated warnings about a threat, first you should update your security software, and then check for any other important information about it in our malware encyclopedia.

Be careful - any files that you exclude will not be scanned, which could leave you open to infection. Only exclude files if you are absolutely sure they are not infected.

To exclude a file from scanning:

  • Open your Microsoft security software.

  • Go to the Settings tab.

  • In the Excluded files and locations section, click Browse and find the file you want to exclude. Click OK.

  • Click Add.

  • Click Save changes. You will no longer be alerted about the file.

Your security software uses definitions to identify threats.

Definitions are also knows as signatures, DAT files, pattern files, identity files, and antivirus databases.

Go to the updates page to download the latest definitions.

Go to Microsoft knowledge base article KB827218 to see which version of Windows you are using.

You might not be able to update because:

  • Malware has disabled your antivirus software.

  • Malware has made changes to your PC so you can’t access the Internet or security-related websites.

  • There are other problems with Windows update.

  • You're using Windows XP. See our Windows XP end of support page.

First, try manually installing the latest updates.

If you still can’t update, go to our advanced troubleshooting page for more help.