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
- UDP: the scanner looks for open UDP ports
- sweep: the scanner connects to the same port on more than one machine
- FTP bounce: the scanner goes through an FTP server 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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