Design Goals

Necessary to establish TCP connection to destination host to retrieve information.

Estimate SSH server deployment by randomly sampling hosts on the Internet.
IPv4 addresses about four billion addresses.
Want to be able to scan addresses quickly even for large sample space.
IPv6 not widely deployed and address space too large for random sampling.

Need to be able to scan specific networks to find vulnerable SSH servers.
Require a way to exclude particular hosts from scans.