Worst-case scenario: the UEd Goblin wipes the map and burns down your house.
The file extension .uz identifies a file, usually an Unreal package, that was compressed by an Unreal Engine 1 game. It is the equivalent to Unreal Engine 2's UZ2 file and Unreal Engine 3's UZ3 file. UZ files are usually stored on "redirect servers", i.e. HTTP servers the game client can fetch packages from that a game server requires.
The .uz format is a general-purpose compression format, i.e. it is not limited to Unreal packages. To compress a file into UZ, run the command
UCC Compress path\to\file.ext
from a Windows command prompt. This will create a compressed file in the same directory that has the .uz extension appended.
To decompress a UZ file, use the command
UCC Decompress path\to\file.ext.uz
and the decompressed file with be created in the same directory but with the .uz extension removed.
Note that UCC Compress and UCC Decompress will override any existing file without warning!
There are also 3rd-party tools for compressing or decompressing UZ files.
(needs clarification) The format of UZ files is relatively simple. It consists of a header and the compressed data:
|UZ File Tag||int (little-endian)||4 Bytes (DWORD)||0x000004D2 (decimal: 1234)|
|File Name String Size||int (little-endian)||4 Bytes (FCompactIndex)||0 - 231-1|
|File Name String||char-array||(needs clarification)|
|Compressed Data||bytes||(needs clarification)|
The compression format is defined by the Zlib library's
uncompress() functions. The entire file is compressed as a single unit.