Simple-minded signature-based malware detection alone isn't enough in the modern world of zero-day attacks and polymorphic malware. The middle panel, the important one, lets you launch a scan for malware. One displays detection history, and one displays real-time protection options, all of which are disabled in the free edition. The rest of the window consists of three rectangular panels. A banner across the top of the pastel-toned main window features silhouettes of mountains, clouds, and a city skyline, adorned with a big message suggesting that you upgrade to premium. I found that the product installed very quickly. The free version is full of subtle and not-so-subtle suggestions to spring for the upgrade to Premium. It does just one thing it cleans up existing malware problems.
In particular, the free edition, reviewed here, doesn't include any real-time protection. If you let the trial expire without upgrading, you'll find that you lose quite a few features.
When you install the free edition, you can choose a 14-day trial of Malwarebytes Premium.