I've just updated to the latest MacOS 10.13.2 and after restarting, my machine asked me to allow incoming network connections for "rapportd".
After blocking it and checking in the firewall config, I can see that this is an executable in /usr/libexec/rapportd which was created on my machine on the 1st of December.
That's a day after I installed the security update 2017-001 (for the second time; autoupdate didn't seem to notice that I'd manually updated it), and I haven't installed or updated any other software recently / around that time. Google Chrome updates whenever it feels like it, so this could be related to a Chrome update (no idea when it last updated).
The internet suggests this is related to some banking protection program but that doesn't seem to fit here, and from a vague text-edit inspection of the binary I can see that it references /System/Library/PrivateFrameworks/Rapport.framework/Versions/A/Rapport (a framework created on my machine back in July and updated in October) which makes me think this is likely to be a new 1st-party OS daemon.
What does rapportd do?

/usr/libexec/rapportd,
/private/var/db/timezone/tz/2019c.1.0/icutz/icutz44l.dat,
/System/Library/PrivateFrameworks/CorePhoneNumbers.framework/Versions/A/Resources/CorePhoneNumbers.ruleset,
/usr/share/icu/icudt64l.dat,
/usr/lib/dyld,
Among others
– geoO Jan 21 '20 at 15:58