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Advanced troubleshooting

Some threats can be harder to remove than others. If you're experiencing any of the following symptoms, you might need to take the additional steps listed on this page:

  • You see warnings about the same threat over and over.

  • Even though your security software says it has cleaned an infection, it comes back again as soon as you restart your PC.

  • Your security software says it can’t fully clean an infection.

  • Your security software gives you an error code.

  • Your security software takes a very long time to complete a full scan.

If you are experiencing any of these problems, you should try all of the steps on this page.

You can also visit the Microsoft virus and malware community to see if someone else has experienced your problem or has a solution.

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Sometimes, Microsoft security software won't work properly if there isn't enough space on your PC's hard drive. A large temporary files folder can also cause problems.

After you've freed up some space, see the next step on updating your software, restarting your PC, and running a full scan.

  1. Download the latest definitions from our updates page.

  2. Restart your PC.

  3. Run a full scan:

    • Open your Microsoft security software.

    • On the Home tab, in the Scan options: area, click Full.

    • Click Scan now.

A full scan can take an hour or more, depending on how many files you have on your PC.

If your security software is warning you about an exploit that isn’t being cleaned, it might be because you are using vulnerable software.

Software that isn’t updated might leave your PC open to infections. Our security software will detect and clean the infections every time they happen, but they will keep happening until you update your software.

Use the Microsoft Safety Scanner

The Microsoft Safety Scanner is a stand-alone tool that comes preloaded with the latest antimalware updates.

  1. Go to another PC that isn't infected and download the Microsoft Safety Scanner onto a blank USB flash drive or CD.

  2. Insert the USB flash drive or CD into your infected PC and run the Microsoft Safety Scanner.

For more help in using the Microsoft Safety Scanner, see the troubleshooting help page.

After you've used the Microsoft Safety Scanner, you should make sure your security software is up to date and run a full scan:

Even if we've already detected and removed this particular threat, running a full scan might find other malware that is hiding on your PC.

Use Windows Defender Offline

Windows Defender Offline is a stand-alone tool that comes preloaded with the latest antimalware updates. It works outside of Windows, which means it can catch and clean infections that hide themselves when Windows is running.

  1. Go to another PC that isn’t infected and download Windows Defender Offline.

  2. Insert a blank USB flash drive or CD into the PC, and then run the Windows Defender Offline file that you just downloaded.

  3. You will be prompted to install Windows Defender Offline to the blank USB flash drive or CD.

  4. After you’ve installed Windows Defender Offline onto the USB flash drive or CD, insert it into your infected PC and restart. You will be prompted to start the Windows Defender Offline tool.

The following articles may help if you're having trouble getting the tool to work:

After you've used Windows Defender Offline, you should make sure your security software is up to date and run a full scan:

Even if we've already detected and removed this particular threat, running a full scan might find other malware that is hiding on your PC.

Most of the time Microsoft security software will remove any malware that it detects. Sometimes you may need to take some extra steps to completely recover your computer or avoid getting reinfected.

You can find this extra information by searching our encyclopedia.

To find a relevant encyclopedia entry:

  • Click on the Get more information about this item online link that pops up in your Microsoft security software when the malware is detected.

  • Visit the encyclopedia and search with the name of the malware that is being detected.

If none of the other steps work, you may need to restore your PC from backup.

After you’ve restored your PC, you should install and update your security software.

To restore your PC from backup:

  1. Restore or reinstall Windows.

    Back up any files and settings you want to keep so that you can restore them later. You'll need to reinstall your programs, so make sure you have the installation discs, product keys, or setup files.

    These articles have more information:

  2. Reinstall security software.

    If you’re using Windows 8.1, your PC comes with Windows Defender built in. Windows Defender helps guard your PC against viruses, spyware, and other malicious software in real time.

    If you’re using Windows 7 or Windows Vista, install security software such as Microsoft Security Essentials or other security software that provides a complete, real-time antimalware solution.

    Keep your antimalware software updated by making sure you have the latest definitions.