Update Minecraft 1.8.4, released on 17 April 2015-year, fixed some security bugs. This update is compatible with 1.8.3 servers.
The number of bugs fixed in update - 8. Below is the list:
1. Now Pets no longer follow players in spectator mode.
2. Vines in the corners of the blocks can now be applied correctly.
3. Fixed incorrect character recognition (game perceived AltGr key as Ctrl).
4. The Lower portals the world no longer put players ahead of them.
5. Fixed bug with cloning objects.
6. The game client is infected with malware, can no longer freeze the server.
7. Entered safe reading NBT data, there's no danger that malware will overwhelm the server memory.
8. Fixed bug where previously joined the user is shown several times.