This ROM is build for O2 network in United Kingdom a carrier branded Samsung Galaxy Y S5363.
This is the official firmware update with build number S5363XXKK3 Android 2.3.6 Gingerbread in Odin flashable stock ROM. This is the same build number as for Czech Republic - O2 version of Samsung Galaxy Y GT-S5363. As you'll notice that the CSC file for UK is 'O2U' while in Czech republic is 'U2C'.
See the version of Czech Republic's S5363XXKK3 stock ROM just to make you out of confusion.
So, only folks in UK can use and flash this stock ROM.
- To check your firmware info type *#1234# on dial pad
This is the firmware update from previous build S5363XXKJ2.
Latest firmware update: S5363XXKK3/S5363O2UKK1/S5363XXKK3/S5363XXKK3
Unit/Model: Samsung Galaxy Y S5363
Product Code: GT-S5363MAAO2U
Country/Provider: United Kingdom - O2
Version: Android 2.3.6 Gingerbread
Build/Released: December 2011
Stock ROM Download: GT-S5363_O2U_S5363XXKK3_S5363O2UKK1
from sammobile.com link