On the WoT's European Advent Calendar there is currently a hidden bonus code, its not complete yet, but this is how you find it...
- Go to Event Calendar
- Click on the Tank of the day
- Press CTRL+A
- Hidden code will appear
This is what's out so far:
This is the code so far: AXTH GH12 BN15
Each part is coming every 7 days so expect to see the remaining part in the last day of the calendar.