Malwarebytes offers a free version that is excellent at cleaning up existing infections. It uses the most current database of threats to scan and remove malware from your system.
Modern malware (like zero-day exploits and advanced ransomware) didn't exist when version 1.70 was released. An old version with a leaked key cannot protect you against current threats. Malwarebytes Anti-Malware 1.70.0.1100 Final Serial Key
If you are looking for Malwarebytes because your computer is currently infected, you don't need a serial key. Malwarebytes offers a free version that is excellent