Frequently asked questions about malicious software

Here are answers to some common questions about malicious software.

What is a virus?

Computer viruses are software programs deliberately designed to interfere with computer operation, to record, corrupt, or delete data, or to infect other computers throughout the Internet. Viruses often slow things down and cause other problems in the process.

What is spyware?

Spyware is software that can install itself or run on your PC without getting your consent or providing you with adequate notice or control. Spyware might not display symptoms after it infects your PC, but many malicious or unwanted programs can affect how your PC runs. For example, spyware can monitor your online behavior or collect information about you, change settings on your PC, or cause your computer to run slowly.

What's the difference between viruses, spyware, and other potentially harmful software?

Both viruses and spyware are installed on your PC without your knowledge and both have the potential to be intrusive and destructive. They also have the ability to capture information on your PC and damage or delete that information. They both can negatively affect your computer's performance.

The main difference between viruses and spyware is how they behave on your PC. Viruses, like living organisms, want to infect a computer, replicate, and then spread to as many other computers as possible. Spyware, however, is more like a mole—it wants to move into your PC and stay there as long as possible, sending valuable information about your computer to an outside source while it is there.

Where do viruses, spyware, and other potentially unwanted software come from?

Unwanted software, such as viruses, can be installed by websites or by programs that you download or that you install using a CD, DVD, external hard disk, or a device. Spyware is most commonly installed through free software, such as file sharing, screen savers, or search toolbars.

Can I get malicious software without knowing it?

Yes, some malicious software can be installed from a website through an embedded script or program in a webpage. Some malicious software requires your help to install it. This software uses web pop-ups or free software that requires you to accept a downloadable file. However, if you keep Microsoft Windows up to date and don't reduce your security settings, you can minimize the chances of an infection.

Why is it important to review license agreements before installing software?

When you visit websites, do not automatically agree to download anything the site offers. If you download free software, such as file sharing programs or screen savers, read the license agreement carefully. Look for clauses that say that you must accept advertising and pop-ups from the company, or that the software will send certain information back to the software publisher.

What's the difference between Microsoft Security Essentials and Windows Defender?

Microsoft Security Essentials is antimalware software, which means that it's designed to detect and help protect your PC against a wide range of malicious software, including viruses, spyware, and other potentially unwanted software. Windows Defender, which is automatically installed with your Windows operating system, is software that detects and stops spyware. To learn more about Windows Defender, visit the Windows Defender website.

Why doesn't Microsoft Security Essentials detect cookies?

Cookies are small text files that websites put on your PC to store information about you and your preferences. Websites use cookies to offer you a personalized experience and to gather information about website use. Microsoft Security Essentials doesn't detect cookies because it doesn't consider them a threat to your privacy or to the security of your PC. Most Internet browser programs allow you to block cookies. For information about blocking cookies in Windows Internet Explorer, see Block or allow cookies.