Using IPv6 with Linux? You’ve likely been visited by Shodan and other scanners

By setting up an IPv6-based network time protocol service most Internet-connected devices rely on to keep their internal clocks accurate, the operators can harvest huge numbers of IPv6 addresses that would otherwise remain unknown. The server operators can then scan hundreds or thousands of ports attached to each address to identify publicly available surveillance cameras, unpatched servers, and similar vulnerabilities.

Within seconds of one of the Shodan's NTP servers receiving a query from an IPv6 device, Shodan's main scanning engine would scan more than 100 ports belonging to the device. The Shodan scanner would then revisit the device roughly once a day.