The act of systematically scanning a computer's ports. Since a port is a place where information goes into and out of a computer, port scanning identifies open doors to a computer. Port scanning has legitimate uses in managing networks, but port scanning also can be malicious in nature if someone is looking for a weakened access point to break into your computer.
Types of port scans:
vanilla: the scanner attempts to connect to all 65,535 ports
strobe: a more focused scan looking only for known services to exploit
fragmented packets: the scanner sends packet fragments that get through simple packet filters in a firewall
sweep: the scanner connects to the same port on more than one machine
FTP bounce: the scanner goes through an FTPserver in order to disguise the source of the scan
stealth scan: the scanner blocks the scanned computer from recording the port scan activities.
Port scanning in and of itself is not a crime. There is no way to stop someone from port scanning your computer while you are on the Internet because accessing an Internet server opens a port, which opens a door to your computer. There are, however, software products that can stop a port scanner from doing any damage to your system.
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Port Scanning This lecture introduce the techniques of port scanning that an attacker may use to discover vulnerable services on an Internet host.
Port Scans Legal, Judge Says Federal court finds that scanning a network doesn't cause damage, or threaten public health and safety.
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