Scanning the whole internet has typically taken weeks or even months.
Here comes Zmap, an open source scanner that aims to knock the same job on the head in less than an hour!
CNET offers a download of the free Nmap software, but not from Nmap's own site. Instead, CNET has wrapped the Nmap installer with a program of its own. On your way to Nmap, you're pushily offered a toolbar first.
Find out why this sort of thing is a Bad Idea.