exploit rogue scanner (type 820)

How do I get rid of this message and ald get my computer working again?

Please download the current version of HijackThis from HERE

• Double click and run the installer.
  
• It will install to C:\Program Files\Trend Micro\HijackThis\hijackthis.exe
  
• After installing, you should get the user agreement, press accept and Hijack This will run.
  
• Select Do a system scan and save a log file. This will open a notepad file of everything Hijack This found, copy and paste it back here.
  

when i go to run HJTInstall.exe I get a security warning window; app cannot execute - the file hjinstall.exe is infected - do you want to activate your antivirus software now?

It never gives me the chance to install?

Try running this first.
Please download exeHelper from one of the two links.
Link 1
Link 2

• Double-click on exeHelper.com or exeHelper.scr to run the fix.
  
• A black window should pop up, press any key to close once the fix is completed.
  
• Post the contents of log.txt (Will be created in the directory where you ran exeHelper.com)
  

Note: If the window shows a message that says "Error deleting file", please re-run the program before posting a log - and post the two logs together (they will both be in the one file).