Malwarebytes switched to subscription with version 2.0 (Announcement:
Introducing Malwarebytes Anti-Malware 2.0!). As Digerati said, there are no lifetime licenses for 3.0. For a while after the release of version 2.0 there were some leftover lifetime licenses from third parties. They were sold in boxed sets that came with a CD and an activation code on a sticker or piece of paper included in the box.
IF this is leftover from before 2.0 was released and comes in a sealed box then it is likely legit. However, if not, don't count on it and be sure there is a guaranteed return if it isn't legitimate.