Is your computer running more slowly than usual? Does it stop responding, freeze often, or display other odd behavior? It might have a virus. Fortunately, if you update your computer regularly and use antivirus software, you can help permanently remove unwanted software and prevent it from being installed in the first place.
Windows Defender (built in to Windows 8), Microsoft Security Essentials, and other antivirus software programs download the latest updates over the Internet to fight new malware. Windows Defender Offline helps protect against advanced malware that can't always be detected by antivirus software.
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Follow the instructions below based on the operating system that your computer is running.
If your computer is running Windows 8, you can use the built-in Windows Defender to help you get rid of a virus or other malware.
Scan your PC with Windows Defender
From the Search charm, search for defender, and then open Windows Defender.
On the Home tab, choose a scan option, and then tap or click Scan now.
In addition to the color codes for your PC’s overall security status, Windows Defender applies an alert level to any suspected malware it detects. You can decide whether to remove an item entirely, research it further, or let it run because you recognize it.
Review quarantined items
If Windows Defender can’t determine whether a detected item is malware or something that you intentionally installed, it prevents the software from running but quarantines it on your PC so that you can decide later.
Windows 7 and Windows Vista
If your computer is running Windows 7 or Windows Vista, do the following:
Run the Microsoft Safety Scanner. The scanner works with the antivirus software that you already have on your computer, regardless of whether the software is from Microsoft.
Download Microsoft Security Essentials for free, and then use the software to run a scan of your computer. For more information, see Help protect your PC with Microsoft Security Essentials. (Note: Some viruses will prevent you from downloading Microsoft Security Essentials. If you can’t download the software, follow the instructions below for using Windows Defender Offline.)
Some malicious software can be difficult to remove. If your antivirus software detects malware but can’t remove it, follow these steps.
Windows XP does not include virus protection.
Click the security icon on the taskbar, or click Start, select Control Panel, and then double-click Security Center to find out if you have already installed antivirus protection from a third party.
Note: On April 8, 2014, Microsoft ended support for Windows XP. This means that there will be no new security updates available through automatic updating for computers that are still running Windows XP.
Also on this date, Microsoft stopped providing Microsoft Security Essentials for download on Windows XP. (If you already have Microsoft Security Essentials installed, you will continue to receive antimalware signature updates for a limited time, but this does not mean that your PC is secure because Microsoft no longer provides security updates to help protect it.)
For more information, see Support is ending soon.
Windows Defender Offline works with Windows 8, Windows 7, and Windows Vista.
Use another computer to download Windows Defender Offline and create a CD, DVD, or USB flash drive with the software on it. Then use the media to restart your infected computer and scan it for unwanted software.
Nothing can guarantee the security of your computer, but there's a lot you can do to help lower the chances that your computer will become infected.
Using a firewall is like locking the front door to your house—it helps keep intruders (in this case, hackers and malicious software) from getting in. Windows Firewall is included in Windows and is turned on by default.
To learn more about firewalls, read Firewalls in versions of Windows.
Microsoft releases security updates on the second Tuesday of every month. Open Windows Update to confirm that you have automatic updating turned on and that you've downloaded and installed all the latest critical and security updates.
You can adjust the security settings in your Internet Explorer web browser to specify how much—or how little—information you want to accept from a website.
Microsoft recommends that you set the security settings for the Internet zone to Medium or higher. (If you use Windows 8, Windows 7, Windows Vista, or Windows XP Service Pack 2 and you use Internet Explorer to browse the web, your browser security settings for the Internet zone are set to Medium by default.)
Internet Explorer also includes a number of features, such as SmartScreen Filter, to help protect against viruses, spyware, and many other kinds of malicious, deceptive, or unwanted software.
To learn more about how SmartScreen technology helps you avoid malware, see the Use Internet Explorer SmartScreen Filter section of this article.
Microsoft Security Essentials helps protects your computer from viruses, spyware, and other unwanted software. It's available as a no-cost download for Windows Vista and Windows 7. For more information, see Help protect your PC with Microsoft Security Essentials.
Note: In Windows 8, Windows Defender replaces Microsoft Security Essentials. Windows Defender runs in the background and notifies you when you need to take specific action. However, you can use it anytime to scan for malware if your computer isn’t working properly or if you clicked a suspicious link online or in an email message.
The best defense against spyware and other unwanted software is not to download it in the first place. Here are a few tips that can help you avoid downloading software that you don't want:
Download programs only from websites you trust. If you're not sure whether to trust a program you are considering downloading, enter the name of the program into your favorite search engine to see if anyone else has reported that it contains spyware. Files that end in the extensions .exe or .scr commonly hide malware. However, even files with familiar extensions such as .docx, .xlsx, and .pdf can be dangerous.
Read all security warnings, license agreements, and privacy statements associated with any software you download. Before you install something, consider the risks and benefits of installing it, and be aware of the fine print. For example, make sure that the license agreement does not conceal a warning that you are about to install software with unwanted behavior.
Never click "Agree" or "OK" to close a window. Instead, click the red "x" in the corner of the window or press Alt + F4 on your keyboard to close a window.
Be wary of popular "free" music and movie file-sharing programs, and be sure you understand all of the software that is packaged with those programs.
Use a standard user account instead of an administrator account. For more information, see Why use a standard account instead of an administrator account?
Don't click links on suspicious websites or in email messages. Instead, type the website address directly into your browser, or use bookmarks.
Don't automatically trust that instant messages, email messages, or messages on social networking websites are from the person they appear to be from. Even if they are from someone you know, contact the person before you click the link to ensure that they intended to send it.
SmartScreen Filter is included in Internet Explorer. If you attempt to visit a website or download a file that has been reported as unsafe, SmartScreen Filter displays a warning that advises you about the potential dangers and enables you to provide feedback.
Application Reputation is part of SmartScreen Filter in Internet Explorer. Application Reputation helps reduce the number of unnecessary warning prompts for most downloads and will display them only when you are about to download programs that are more likely to be malicious.
Windows SmartScreen is built into the Windows 8 operating system. If your computer is running Windows 8, Windows SmartScreen Application Reputation can help protect you from downloaded programs that are more likely to be malicious. You can adjust Windows SmartScreen settings to suit your preferences for dealing with unrecognized apps.
Skype also uses SmartScreen technology. For example, if you're using Skype and you click links to websites that are known to contain malware and phishing threats, Skype blocks the sites.
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