A few days ago, on April the 16th, 2019, Six Apart made available 3 movable type releases.
All these releases, contained a security fix and some of them came available with a number of new and improved features.
Movable Type v6.3.9 contained just the security fixes as that product series is going to reach its 'end of life' cycle next month, on May 16th, 2019. After that date, for one more year, Movable Type v6.3.x will continue to get only security fixes. Then, from May 16th, 2020, the product won't be supported anylonger.
The great next for those that are not yet ready to adopt Movable Type v7.x is that Six Apart just launched Movable Type v6.5 which is basically Movable Type v6.3.9, but with a consistent number of new and improved features. Six Apart is trying to continue the movable type v6.3.x development through movable type v6.5 and this other product is meant to last until 2022.
Movable Type v7.1.2 contains a consistent number of new and improved features and it shows how involved is Six Apart in further developing Movable Type.
Comparing to Movable Type v7, which was by itself a huge step forward from movable type v6.x in many respects, Six Apart launched v7.1 and now v7.1.2, both containing a very large number of new and improved features.
I would strongly recommend upgrading to Movable Type v6.5 or to Movable Type v7.1.2.
You could read more about them and even test them for free from the Movable Type Demo website initiative, at: