Windows Defender is a real-time monitoring system that protects your PC from spyware and other unwanted software. It helps maintain your operating speed by getting rid of threats that slow things down, change computer settings, and open pop-up windows. Defender will detect and, with your consent, remove spyware that it identifies during its scheduled scans. These scans happen in the background of your computer so you still have complete computer functionality.

Even though Windows Defender has been all but replaced with Windows Live Essentials, many PC users, and especially users of Windows Vista, still run Defender and encounter its error codes.  This article is for anyone who encounters error 0x8050800c, no matter what system they're running.  It will give you the fundamental how-to you need to trace the source of the error and eliminate the problem in no time.

The 0x8050800c Windows Defender Error Code: What is it?

“Windows Defender encountered an error:0x8050800c. An unexpected problem occurred. Install any available updates, and then try to start the program again. For information on installing updates, see Help and Support.” If you are seeing this, there is obviously a problem with your Windows Defender program.

Dealing with the Error 1 - Fix

Is It Even Turned On?

Windows Vista comes automatically with Windows Defender, however in some systems Defender isn’t turned on. To find out if this is the case with your system:

1. Go to your Start menu and type “Windows Defender” in the search field.
2. If a pop-up window opens saying “Windows Defender is turned off…” just click on the “Turn on and open Windows Defender” link at the bottom of the window.

Update

If it is on, the first line of defense of error 0x80… is to update your version of Windows Defender for Windows XP or Vista operating systems. You can do this in one of two ways. You can either open Windows Defender and click on the Update option, or you can visit the Windows Defender download page to get the latest and greatest version.

Reinstalling

And if it still doesn’t work? This is where it gets tricky. If the update doesn’t work the next step is to go into your system’s registry and change things. This is always the last step you want to take, the proverbial Hail Mary pass if you will. As you know, it’s not exactly a good idea to start messing with your Windows registry. Bad things can happen if you delete the wrong file, or mistype a command. So always use registry editing as your last ditch effort. If I haven’t scared you away yet, here’s how you do it…

1. Go to your Start menu and type Regedit in the Run search field.
2. When the Registry Edit window opens you’ll want to scroll down to find: HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\Current Version\ProfileList
3. Click on the plus sign next to ProfileList to see a list of entries that start with S-1-5.
4. Click on each S-1-5 line and look to the right. They should all have a file that says “Profile Image Path” and “REG_EXPAND_SZ.

5. If any of them do not have a Profile Image Path entry, you need to right click in the window and choose Expandable String Value.

6. New name the automatically named New Value #1 by right clicking on it and click Rename.
7. You’ll want to call it ProfileImagePath. Do this for all S-1-5 entries that do not have it.
8. Exit out of your registry and restart your PC. Don’t touch anything else in the registry!!

Dealing with the Error 2 - Replace

Upgrading to Windows Security Essentials for Free

Windows Defender was well supported, and was the primary security offering from Microsoft when it released Windows Vista.  Today, however, Microsoft has minimized its support of Defender in favor of a new application:  Microsoft Security Essentials.  Essentials is part of the Windows Live framework, Microsoft's answer to a completely online arena where users can integrate mail (Hotmail), online storage (SkyDrive) and online defense (Security Essentials).

If you're not overly attached to Windows Defender, but want a free (and highly-rated) security program, you can always opt to upgrade.  Windows Live Essentials is available free to every user of Windows, no matter what version it is.  You can get Security Essentials here.   Just be sure to uninstall Windows Defender before you upgrade to Security Essentials.  You can uninstall it by typing Windows-Key + R.  This opens the Run Menu.  Here, type in appwiz.cpl, or open the Add/Remove programs dialog in the control panel.  Once the dialog is open, scroll through the list until you find Windows Defender and then select to uninstall it.  Don't worry about alerts telling you that your computer won't be secure since you're going to install Security Essentials as a replacement.