Avast Free Manual Update

I recently installed Avast Free Antivirus 2016. When I manually updated the virus definitions in the settings window, the program updated from 12.3.2280 (build 12.3.3154.0) to 12.3.2280 (build 12.3.3154.19).

http://static.avast.com/support/kb/images/v12/avkb22/en/settings_update.png

How can I update the virus definitions without updating the program?

I rather use the offline installer to update the program.

Right click the avast icon near the clock > update definitions
or
download the offline VPS and use that

These are uUpdates that get delivered with the VPS.
You can’t stop it, as it’s used for bug fixing.