Realgoldsoft Baku Frozen computer, popup ad said computer infected,advising security tool. unable to get off screen until credit card # entered. unknown, Internet

I had begun having problems with my computer being slow, and shutting down a lot. Then I started having pop-up ads advising I needed to update my "security tool". I have virus protection on my computer, but my computer was locked up and the virus protection program was unable to be opened. A window opened stating I had multiple critical level viruses, and that files were being destroyed. The only thing that would take an entry or work at all was the option to buy the virus protection that was being offered. After putting in a credit card number, the screen unfroze and stated there were no viruses. I was then able to access my 'authentic' virus protection, and clean my system, but my computer is still slow and shuts down on my occasionally. I have started having the pop-ups again, and my credit card company tells me they have no address or phone number of this company, and that usually any charge comes with an address and phone number of the company.