"A port scan or portscan is a process that sends client requests to a range of server port addresses on a host, with the goal of finding an active port; this is not a nefarious process in and of itself. The majority of uses of a port scan are not attacks, but rather simple probes to determine services available on a remote machine." - Wikipedia
"Port scanning is an ideological ambiguity within the computer industry. While usually considered malicious, port scanning is often used by system administrators to diagnose problems on their own network. While most private organizations prohibit the activity, there are currently no state or federal laws that specifically address it." - The ethics and legality of port scanning.
"Court holds that plaintiff's act of conducting an unauthorized port scan and throughput test of defendant's servers does not constitute a violation of either the Georgia Computer Systems Protection Act or the Computer Fraud and Abuse Act." - VC3 vs Moulton
Lets say someone decided they wanted to port scan the entire internet. Is this port scan illegal?