If you've never had someone contact you to stop (spamming|scraping|crawling|DOSing) their web service, then you're not experimenting enough.
That said, once they ask you to stop, it's the decent ethical thing to simply stop :)
That said, once they ask you to stop, it's the decent ethical thing to simply stop :)
http://nmap.org/book/legal-issues.html
There are a lot of thoughts on this subject over on the nmap.org site on messing around with data on someone else's computer, be that a private or public service.
Someone ran a port scan on my IP and noticed port 5900 was open and decided to connect to it, I had my computer configured to automatically accept connections (because I use the iPhone VNC client as a remote control), I was quite glad I was using my computer at the time and noticed them connecting!
My first reaction was to run NMAP against there IP, I guess thats probably a bad move!