There are a number of rollback plugins you can install, if you are using Bukkit or Spigot. These plugins log almost everything that your players do on your server and can individually rollback or undo the actions of specific players, groups of players; and can also tell you who has placed or removed blocks, among many other features.
If you are running a public server, and are worried about griefers – you should install one of these plugins right away!
Here is a selection of popular rollback plugins:
If you don’t know how to install a plugin, please read our helpful guide on installing Bukkit plugins.