HELP!!!! ANTIVIRUS SYSTEM PRO VIRUS!!

i don't know how i got the stupid antivirus system pro virus thing on my computer, but now i can't get rid of it!!!!
i followed the steps and ran malwarebyte's anti malware, but it's still there! and it's making all sorts of ads pop up on internet explorer, like porno.com and adult.com! (i use firefox, btw!)

HELP PLEASEEE!!

Hello ashley125,

Welcome to Geek Police, my name is Origin and I will be helping you today. Please keep the following in mind:

• If you do not get a reply from me or another helper within 2 days, please reply to your topic with the phrase BUMP
  
• If you have any cracked/pirated software in your computer delete them or we will not help you.
  
• Only follow advise from Geek Police Staff and not a regular member.
  
• Do NOT run any tool without Geek Police supervision as it could hinder your system useless.
  

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.