There is only one file type that uses the .NUP extension:
Smart Security Update File
A NUP file is an update file used for updating ESET Smart Security, a personal firewall, antispam, antivirus, and antispyware program. It contains the update name, software version and build, category, date, file size, and the update module data. NUP files are also used by other ESET products, including Cybersecurity for Mac.
ESET Smart Security was replaced by ESET Internet Security, an improved security program. It features multi-layered security for Windows users as they browse the web.
Updated: January 17, 2017