There is only one file type that uses the .UDEB extension:
Debian Package File
Package format used by Debian, an open source computer operating system based on the Linux kernel; contains a minimal amount of essential software files; commonly used in bootstrapping Debian; saved in the same format as .DEB files, but cannot be installed on a traditional Debian system.
UDEB files are also called "micro debs" since they contain only the essential files for software execution.
Updated: June 19, 2010