You actually don't have to understand everything they're talking about on these sites. All you have to know is that your computer has many ports through which it communicates with other computers on the net.

Hackers also use the ports to attack your system (read, modify, even delete your files, or worse: to attack other systems, perhaps big corporations, using your identity). They use programs that scan many computers at the time, in selected areas or countries. Internet Service Providers usually don't take responsibility, so if somehow your computer was used for unlawful activities YOU are to blame.

ShieldsUp is a site that checks your system for such attacks. It checks some of the sensitive ports that are usually used by hackers, but not all of them (at least not yet), and actually do not offer you protection: they merely make you aware of your vulnerabilities.

The BEST protection is provided by firewalls; 2 types: hardware (another computer), and/or software (special programs). Both types can be very expensive, depending on your needs. The price can be as high as thousands of dollars.

ZoneAlarm is a free firewall program provided by Zone Labs, and controls all communication ports in your computer. Besides logging all external attacks, it also asks your permission for each program installed on your system that is sending information to outside sources (some of them are trying to communicate without your knowledge).

One other advantage: the ports on your system can have one of three states: OPEN (completely vulnerable), CLOSED (inaccessible, but existent), And INVISIBLE (inaccessible, and also non-respondent - doesn't respond to outside requests, thus it appears as if your computer is turned off). Not only a firewall makes sure your computer is INVISIBLE, but it also delays the scanner programs used by hackers; the more protected computers, the longer scanners take to do their job.

So, for now, the only and the best thing you can do for your protection is to install a firewall.