As explained by Metaquotes (not really much of an explanation or proper change-log though)

New MetaTrader 4 build 1170
The MetaTrader 4 platform update will be released on December 20, 2018. The update fixes errors and improves the platform stability.

We remind you that support for older versions of operating systems, including Windows XP/2003/Vista, has been discontinued. The minimum acceptable OS version for the client terminal is Windows 7.

The update will be available through the Live Update system.

I guess the real test will be when the market opens again.

A few problems noted so far by some users:

• Tick Data Suite back-test with kernal 32 dll import failing since 1147.
• Attempting to read a HST file seems to offset the expected results.
• Web-updates are breaking compatibility & freezing the terminal.
• Certain EA's not working.
• Terminal freezing on profile change.