Nero BackItUp compressed backup file
NCO is a file extension for a backup file created by Nero BackItUp.
NCO files contain a backup of files to be written to a CD or DVD. NCO files use ZIP compression, may also be password protected and encrypted with a 56-bit key. NCO files can be opened by compression utilities such as WinZip if they are not encrypted. NCO files can only be opened by Nero BackItUp if they are encrypted.
Learn more about .NCO files:
Visit the Nero web page.
Read about backup at ITKnowledgeExchange.com.