identd
There are a number of different software packages out there that do port and service-based scanning of machines or networks. SATAN, ISS, SAINT, and Nessus are some of the more well-known ones. This software connects to the target machine (or all the target machines on a network) on all the ports they can, and try to determine what service is running there. Based on this information, you can tell if the machine is vulnerable to a specific exploit on that server.
SATAN (Security Administrator's Tool for Analyzing Networks) is a port scanner with a web interface. It can be configured to do light, medium, or strong checks on a machine or a network of machines. It's a good idea to get SATAN and scan your machine or network, and fix the problems it finds. Make sure you get the copy of SATAN from metalab or a reputable FTP or web site. There was a Trojan copy of SATAN that was distributed out on the net. http://www.trouble.org/~zen/satan/satan.html. Note that SATAN has not been updated in quite a while, and some of the other tools below might do a better job.
ISS (Internet Security Scanner) is another port-based scanner. It is faster than Satan, and thus might be better for large networks. However, SATAN tends to provide more information.
Abacus is a suite of tools to provide host-based security and intrusion detection. Look at it's home page on the web for more information. http://www.psionic.com/abacus/
SAINT is a updated version of SATAN. It is web-based and has many more up-to-date tests than SATAN. You can find out more about it at: http://www.wwdsi.com/~saint
Nessus is a free security scanner. It has a GTK graphical interface for ease of use. It is also designed with a very nice plugin setup for new port-scanning tests. For more information, take a look at: http://www.nessus.org
identd