The "Universally unique identifier", or UUID, identifies a consistent format for any unique ID to be used. The UUIDs are 128 bit long. UUID v1 is generated by using a combination of 48-bit MAC address of the host machine and the current time and date.
UUID Version 1 (v1) Uniqueness
The UUID v1 makes use of combination of 48-bit MAC address of the host machine and the current time and date, it is always unique unless it is generated multiple times on the same host machine at the same exact time. Also as the UUID v1 makes used of the the host machine address and date and time, some part of the UUID's will be the same and this may result in the user indentifying the underlying host machine address and the date time where the UUID v1 was created.