1) You may have downloaded it knowingly or unknowingly mistaking it to be something else.
2) It may have automatically downloaded while you were visiting some harmful website
3) Your computer may have a trojan virus which in turn downloads such an application.

Recently I have noticed that the malware authors are also keeping track of the removal instructions published on the internet. As soon as they think that the malware is exposed, they change the file/folder names and the locations where they are saved on the hard disk. So keeping this in mind you will require the latest information of the malware in order to be able to remove it.

It is also reported at S!Ri.URZ blog that  The Trojan-Downloader uses 2 files, the rogue installer and a trojan fake alert. This new version also comes with a RootKit and it patches files in memory: (dump_atapi.sys and dump_WMILIB.SYS). If that happens then there will be a virus component running in the memory while you are trying to remove it.  If you are unable to search and delete its files as mentioned in this article, try to do a memory scan using your antivirus application, Also do a scheduled boot time scan in order to find and delete the virus infected files, during the boot time. Usually most of the antivirus applications do a memory scan as well as a scheduled boot scan. 

You can find latest ThreatExpert analysis reports of this rogue on this link

If you happen to have the rogue installer, you can submit it to threatexpert site and get it analyzed. That will help you to get the precise information about the virus.  

 Files Associated

 These are the different EXE file names that are used in this malware

Trying system restore

If you know the duration since your computer is infected, you can try to restore your computer at a prior date, that will work like a miracle in removing the infection

• Using system restore in windows XP
  •          Using system restore in windows Vista

Free removal tools

• Special tools to remove a single virus or a family of virus.
• Free Online virus scanners
• Fully functioning antivirus/ antispyware

•  Free tools for windows XP
  
  
  • Free tools for windows Vista

Manual Removal

These are the steps to be taken, if you want to or need to remove the infected files manuall. You may not find all the files that are mentioned below on an infected computer. The virus adds different files depending on its variation. I have listed all the names found in the reports available. 

Boot in safe mode

Sometimes you will not be able to delete a file even if you find it, in that case you should boot in safe mode and then try to delete it/ them.

• How to boot in safe in windows XP

• How to boot in safe mode in windows Vista

 Remove Processes from Task Manager 

Press Ctrl Shift Esc to open Task Manager. See in the list of the processes for SaveDefender.exe, SaveDefenderSvc.exe, and a random looking name  Select and press End Process button, Confirm to terminate the process and Close Task Manager.

Alternately you can use Windows Defender to see the path of a currently running program/ process and its publisher, so as to differentiate malware processes from processes belonging to legitimate publishers. You may find such processes listed under Unknown Publisher in windows defender.

• How to use Windows Defender in windows XP
  
  
  •         How to use Windows Defender in windows Vista

• How to use Sysinternal's Process Explorer 

Removing entry from windows startup

The system configuration can be started in xp and in vista by typing msconfig in the run box/ start menu search box. In xp by clicking on Start > run . The windows startup is reversible, therefore you can check / uncheck any entry from windows startup any number of times.

After the system configuration window is open, Click on the Startup tab, that will list all the programs that are scheduled to start with windows. Expand the middle column using your mouse pointer so that you can see the full path of the program. Locate and uncheck  "SaveDefender", "SaveDefender Software" or SaveDefender.exe, SaveDefenderSvc.exe, and any random looking name (look for any other suspicious names)  Press Apply , Press Close/Ok , Select  "do not restart" at the next prompt.

Removing windows Service

This malware creates a new windows service named "SaveDefenderSvc" or SaveDefender Security Service. By default is is stopped. This service can be removed after deleting the file "SaveDefenderSvc.exe" and then removing it from the registry, easily done by running CCleaner.

 View Hidden Files

Before you could delete SaveDefender and its associated files you need to search for them, and before doing that you need to enable to view hidden files and folders 

•  How to Enable to View Hidden Files and Folders in Windows XP
  •         How to Enable to View Hidden Files and Folders in Windows Vista

Deleting files

After restarting the computer, use the windows search utility to search for "SaveDefender" and also search for the names that you found and removed in the task manager or in the startup list. This search should find all its folders on the hard disk , delete the folders from the hard disk. 

These are some folders that were found on different infected computers.

 Run CCleaner

After deleting SaveDefender and its associated files , as there will be leftover entries in the windows regitry. CCleaner is a free temp files/registry cleaner, that will automatically clean the registry as well as remove the temp files . Click here to read more

 Edit Registry

if you are comfortable in using the regedit command. You  can find the registry modifications in any of the reports mentioned in the begining of this article.

• How to edit registry in windows XP
  •           How to edit registry in windows Vista 

More Problems

If you are unable to open Task Manager, registry editor, system restore, Folder Options etc

If the virus has disabled them. There are free tools and techniques to solve this problem.  They are listed here.

Tools for Windows XP

Tools for Windows Vista

Use the system file checker

If you want to make sure that the windows system files are not altered by the virus, and in case if they are altered then to repair them.

•  How to run System File checker utility in windows XP
  •          How to run System File checker utility in windows Vista

Unable to access security related sites

Using Firewall

Check your firewall for any suspicious communication from your computer to the internet and block it using firewall.

Communincates with the following sites

• SaveDefender.com
• 91.212.127.131 port 80

 Reprinted with permission from ThreatExpert.com