Malware Removal

A program named "Best Malware Protection" keeps showing up on the screen of my computer, telling me that I have numerous infections and viruses. When I ask it to remove these, it immediately goes to a box that asks for my Visa card number and requests that I pay $69.95 for the system to remove these so-called viruses. I have a commercial protection system (McAfee) that says I do not have any viruses even though "Best Malware Protection" say that I do. I will not pay them anything. I do not know where this came from and I want it removed. It continues to pop up unexpectedly and interfers with my work and other activities, and I cannot remove it with my current abilities.