i installed windows defender and all went well until trying to update. i have xp pro and have the auto update on. i ran a serch for signatures and none came up. i also went to windows update and had no results. hope someone can help. thanks, Mackd

Is Windows Defender in your list of programs? If it is, open it and click on the small arrowhead next to the Question mark at the top of the main WD window. Choose update.

yes, also on my taskbar and when i right click to open it , check for updates comes up. when i click ti , ti grays for a secomd and nothen happens.

Sounds like a bad install. Does WD show up in the Add/Remove list? If so, remove it and reinstall.

i have reinstalled 3 times. i also redownloaded it again and the same problem occured.

Check out the info in the link below. I have not used the uninstaller mentioned but have read on this site about success with it.
http://support.microsoft.com/kb/290301

i used microsoft windows cleanup to remove program and signatures and reinstalled. still nothen happens.

Could be malware. Below are two good programs to scan with. Scan with the AVG antispyware in safe mode after installing and updating. Let it quarantine whatever it finds.
The other is Windows One Care. It will scan for malware, clean your logs, temp files and registry. It will also defragment your harddrive.
http://free.grisoft.com/doc/avg-anti-spywa...e/lng/us/tpl/v5

http://safety.live.com/site/en-us/default

Please let us know what if anything is found by the scans. Did Windows offer any explanation as to why the install failed?

i went to safe mode and scanned with avg spyware and ewido , harddrive is clean. ti is hard to get any help from microsoft.

The link below is to a site that will instruct you on how to reinstall Windows Installer. That might be the next step if you are still having a problem. Have you used the installer for anything since attempting to install Defender?
The reinstall instructions is toward the bottom of the page. I had a problem viewing the page in Firefox so used IE. http://support.microsoft.com/kb/324516

i diid the procedure on the windows reinstall installer. no luck there either . i may haft to forget wd and use other anti spyware.

Sorry nothing has worked. I am out of ideas, also. Were you able to defrag your harddrive?
If you have Spybot Search and Destroy with TeaTimer enabled, it is almost the same as Defender. I would also suggest to install Spyware Blaster. One Antivirus and a good firewall such as Zone alarm free.
AdAware Free is also a good program to keep on your comp.
With the programs listed above and good surfing habits you should have no problem. Most get into trouble with clicking links in emails and visiting unsafe sites. Another suggestion I would make is to use another browser other than IE. Firefox with NoScript extension will keep you from getting hit in a driveby on the web.
Maybe someone else will come up with an answer to why you can't install Defender.

i finally got the update to work. i want to thank you for all your help. maybe this will help someone in the future. i went to start and run. typed in regsvf32MSXML3.dll. thanks again, Mackd