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. You can see several latest analysis reports 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.   

 Family

The other similar fake applications are Braviax family rogues - Home Antivirus 2009, Home Antivirus 2010, PC Antispyware 2010, PC Security 2009

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 manually

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 a processe/s named "AntivirusPro_2010.exe"  select if found and press the End Process button, confirm and then close the Task Manager.

 Optionally 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 windows genuine processes.

• 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  "AntivirusPro_2010"  (look for any other suspicious names)  Press Apply , Press Close/Ok , Select "Restart the computer" at the next prompt.

 View Hidden Files

Before you could delete Antivirus Pro 2010 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 "AntivirusPro_2010". This search will find all its folders on the hard disk , delete the folders from the hard disk. 

 Run CCleaner

After deleting Antivirus Pro 2010 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 a list of all the registry modifications done by different variations of this rogue on this link.

• 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.

More help

Download/ install and run a free tool called TrendMicro Hijackthis. This program will generate a logfile "hijackthis.log" save it and mail it to support(at)comprolive.com for analysis.