Let me assist you with this.
First we have to know what really happened before the infection.
Did you receive any popup message on your browser or receive calls telling you that your computer is infected?
If yes, what did you do after getting the popup message or call? Did you allow or contacted the support line presented on the message or allowed the person who called you to remotely access your computer?
Because it seems to me that the case that you have is one of the million Technical Support Scam case. Basically, if someone (fake support) got the permission that he needs on your computer to remotely access it, there's nothing that our program can do for that since he got the full control already, he can easily disable the program and install the threats or malware that he wants to install so he can get a bragging rights for you to pay the amount that he will request from you.
Providing the case history will be a great help for us so we can give you the answer to your questions.
I hope this helps.
Thank you and have a great day!
Trend Micro Home Users Community
Hi dmstengel! To the above answer I'd like to add that you start a "community membership" here at the Trend Micro Home Users Community. We've heard this scam related here so many times in the last year or so that it is quite incredible it's still around. But, when you sign up for membership, you receive emails when someone has a problem with their security or computer/device, whatever. You gain knowledge BEFOREHAND and are aware of how to deal with that problem from the experience of others, and the solutions to them from the Trend Micro technicians, like TM_Jabi above, and many others.
Knowing the experience of others, you are less likely to become a victim of the "bad guys". It's worth giving it a try!
" In July, my computer was taken over by "Microsoft tech. support" and cost me $649.49"
Your computer was not "taken over", you deliberately offered access to your computer to the fake "Microsoft tech. support" and further more , you provided a credit card number from where the money were paid.
So, I do not see how any software in the word can help in this situation.