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.

eSecurity Planet 
A resource for daily information on e-security targeted to IT managers. The site provides users with information from a variety of sources, including experts at security product and services firms, and the consultants who follow the security industry.

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.

SecurityTracker.com
Information on the latest security vulnerabilities, free SecurityTracker Alerts, and customized vulnerability notification services.