i went ahead and bought malwarebytes. as well as avast, however i meant to install avast on my other computer, but in a daze of idoicy i installed both on my more expensive computer.
any ways, unless you literally only have a couple dollars to your name its worth it to purchase the software, its good for a year or two i think.
also, i very much doubt the free trial version updates itself after the time has expired, even if its still letting you use it. in a few months down the road the trial version will be useless since it won't be blocking any of the new malware thats been developed by cyber criminals.
I've never used the free trial myself, but I'm guessing that that's it. They probably let you use it indefinitely, but stop giving you updates, which makes it useless. I think you're best off going back to the free MBAM and use the free Avast for real-time protection. Works like a charm for me, and you won't have to purchase anything.
Edit: I use 'probably' too much.