Astrolopithecus

I have an official purchased version of SAS, update definitions regularly, and run the program automatically upon boot. However, I have gotten two viruses in the past week! I managed to pick up RootKit (TDSS), and Security Shield, in spite of having SAS. SAS didn't prevent the viruses OR remove them; I had to dig around and find other software to do the job, and it wasn't easy! I am quite dissatisfied with the performance this product. What is the deal?