There are numerous public domain tools that do this, so the cat is already out of the bag.
Last I read about it, you can scan the entire IPv4 space for a port in about 40 minutes providing you have the bandwidth and a forgiving ISP. I see another comment claiming a tool can do it in 6 minutes. Easy at "apt get install" and a single command.
Note that "scan the internet in 6 minutes" only means this tool is capable of generating packets fast enough on the host machine to theoretically do a 6 minute scan. In practice, the NIC, home network, and local ISP connection will bottleneck and the scan will be orders of magnitude slower.
Last I read about it, you can scan the entire IPv4 space for a port in about 40 minutes providing you have the bandwidth and a forgiving ISP. I see another comment claiming a tool can do it in 6 minutes. Easy at "apt get install" and a single command.