Most of the better FREE anti-spyware programs I know of, come without real-time protection. Hence, no "blocker". Paid versions do.
You will find many of the members use SUPERAntiSpyware and Malwarebytes' Anti-Malware. They both offer free and paid versions.
I realize you asked for a "blocker". If you don't wish to pay for either, they can (at the very least) be used as stand-alone scanners.
What is the best free program to block spyware/malware?