Microsoft Windows AntiSpyware has been discountinued for Windows Defender, download it here:

Known spyware on your PC can be detected and removed. This helps reduce negative effects caused by spyware including slow PC performance, annoying pop-up ads, unwanted changes to Internet settings, and unauthorized use of your private information. Continuous protection improves Internet browsing safety by guarding over 50 ways spyware can enter your PC.

Since releasing Windows AntiSpyware (Beta) on January 6, 2005, we have received feedback from customers and have made enhancements to the software based on this feedback. We have enhanced some of the real-time protection agents, added new threat categories, and improved stability and performance. If you are using a previous version you can simply upgrade to the refreshed version. The version number of the refreshed version is 1.0.509. To check the version number, click About Microsoft AntiSpyware… on the Help menu.

Participants in the worldwide SpyNet™ community play a key role in determining which suspicious programs are classified as spyware. Microsoft researchers quickly develop methods to counteract these threats, which are automatically downloaded to your PC, so you stay up-to-date.

The user must be an administrator to install this application.

What's New:

Improvements in the current build

Provision of information about processes running on a PC

This refresh solves an issue with the way Windows AntiSpyware (Beta) displays information about processes running on the PC. Specifically, the solution fixes the display of Running Processes on the System Explorers feature (on the Tools menu, click Advanced Tools, then click System Explorers).

Signature delivery

An issue has been solved that prevented some customers from receiving complete anti-spyware signatures in recent weeks.

New anti-spyware signatures

New signatures available with this refresh address the most recent threats that we've identified, based on feedback from members of the SpyNet™ community and the work of our anti-spyware research analysts.

Microsoft would like to encourage all Windows AntiSpyware (beta) users to download and install the new update (Build 1.0.615).

Known issues

Potential issue with Windows Media Center Extender

There is an incompatibility between Windows AntiSpyware (Beta) and Windows Media Center Extender. If you install Windows AntiSpyware (Beta) on a computer running Windows XP Media Center Edition 2005, Windows Media Center Extender cannot establish a remote connection. If you want to connect to a Windows Media Center Edition 2005-based computer by using Windows Media Center Extender, uninstall Windows AntiSpyware (Beta). For more information, see the KB article at;en-us;892374.


If you see a dialog box with the following message after you start your computer or when you start Windows AntiSpyware (Beta), you need to repair or reinstall Windows AntiSpyware (Beta). The following message can also refer to Error 102 or Error 103:

"Warning: Microsoft Windows AntiSpyware has encountered a critical error (Error 101). Please restart Windows AntiSpyware and run the program again. If you continue to experience this problem, please uninstall the program and install the most recent version of Windows AntiSpyware. You can use Add or Remove Programs in Control Panel to uninstall this version of Windows AntiSpyware."

You can repair Windows AntiSpyware (Beta) using Add or Remove Programs in Control Panel. Click Microsoft AntiSpyware and click Change. Click Next, and then click Update.

If you see the critical error message again, uninstall Windows AntiSpyware and reinstall it. To do this, use Add or Remove Programs in the Windows Control Panel. Click Microsoft AntiSpyware and click Remove. You can reinstall Windows AntiSpyware (Beta) from the beta download page.

The spyware scan removes sites added to Restricted Sites security zone in Internet Explorer. If you have added Web sites to the Restricted Sites security zone to prevent access to them, we recommend you make a backup copy of the site list before running Windows AntiSpyware (Beta).

Windows AntiSpyware (Beta) may prompt you to remove some peer-to-peer (P2P) file sharing programs. If you choose to remove such a program, Windows AntiSpyware (Beta) deletes the entire contents of the Program Files directory that relates to the P2P program. Because some P2P programs store downloaded files in a default directory under Program Files, this might remove all files downloaded through the file-sharing program. For example, KaZaA stores .exe and .dll files at C:\Program Files\Kazaa. Downloaded files are stored at C:\Program Files\Kazaa\My Shared Folder. If you use Windows AntiSpyware (Beta) to remove KaZaA, all files and folders under C:\Program Files\Kazaa are removed. If you have installed any P2P file sharing programs, we recommend that you make a backup copy of your downloaded files before running Windows AntiSpyware (Beta).

You do not need to uninstall other anti-spyware or antivirus programs to run Windows AntiSpyware (Beta). Other programs or Windows AntiSpyware (Beta) may prompt you to allow or block an action, but there are no other known incompatibilities with other anti-spyware or antivirus programs.