ShieldsUp!
There’s a really neat web-based application on the Internet called “ShieldsUp!“, which allows you to test out how safe your computer is from intruders on the Internet. When you run the program, it scans all of your Internet ports to check which ones are open and displays a report to show how secure your computer or network is from intruders. It’s a very safe program to use and was designed by Gibson Research Corporation.
Gibson Research Corporation also designs other interesting free security software, which are worth checking out.
