A reader tells us that he uses Windows Defender to scan his computer for adware and spyware every other day. So far it has reported finding no problems.

However, he writes, he also scans his computer with two other antispyware programs -- Ad Aware and Spybot Search and Destroy. Both have reported that he has adware on his system. What gives?

The answer might lie in how Windows Defender and other antispyware products actually define spyware. For example, Windows Defender doesn't detect cookies. Why? Because many cookies are used for legitimate purposes and Microsoft believes that the appropriate place to manage cookies is through your Web browser.

This is a complicated issue, because new forms of spyware are developed every day, and some components of legitimate programs can meet criteria for spyware, if a program defines spyware broadly.

If you're interested in how we define spyware, take a look at How Windows Defender identifies spyware and Windows Defender antispyware cycle .

It might also be the case that the version of Windows Defender he is using hasn't been updated lately. Windows Defender detects spyware by using what we call "definitions."

These definitions need to be updated in order for Windows Defender to work correctly. Updating them is a snap if you have Automatic Updates in Microsoft Windows turned on, because Windows Defender works with Automatic Updates to automatically install the latest definitions.

To make sure that you have Automatic Updates turned on, click Start, click Control Panel, and then click Performance and Maintenance. Click System, and then click the Automatic Updates tab and review the settings.

Instead of waiting for regularly scheduled updates from Windows Update, you can also tell Windows Defender to check for new definitions automatically before scheduled scans. Here's how:

1.       Open Windows Defender by clicking Start, clicking Programs, and then clicking Windows Defender.

2.       Click Tools, and then click Options.

3.       Under Automatic scanning, make sure the Automatically scan my computer (recommended) checkbox is selected.

4.       Select the Check for updated definitions before scanning check box, and then click Save.

If you try these steps, but it still looks like Windows Defender has made a mistake, you can report a possible spyware problem to Microsoft.

Windows Defender is no longer in beta! The most recent version is available now at the Microsoft Download Center.

A reader recently wrote us to say that Microsoft Windows Security Center was telling him that he had no antivirus software installed. He had finished his free trial of Microsoft Windows Live OneCare and removed it and then installed Microsoft Windows Defender, thinking it would protect his computer from viruses.

Windows Defender helps protect you from spyware, but it’s crucial that you also have antivirus software to help protect you against viruses.

What's the difference?

·          Spyware and adware  collect information about you without appropriate notice and consent. 

·          A computer virus spreads software, usually malicious in nature, from computer to computer. 

Spyware can get installed on your computer in a number of ways.  One way is via a virus. Another way is for it to be secretly downloaded and installed with other software you've chosen to install. You and I both know how easy it is to skip reading all the documentation on a free program and just click "OK." That's often how they get you.

In short, spyware is a specific type of unwanted software that covertly collects your information. A virus is a specific way software can be covertly distributed, often by e-mail.  Both spyware and viruses can cause damage to your computer or cause you to lose important data.

Now it’s time to start protecting yourself from both.  To help protect against spyware, try Windows Defender. For viruses, consider Windows Live OneCare  or software from another antivirus provider.