After a while, I decided to install GUI for the Linux firewall called Firestarter.
What is interesting, that constantly, your computer is being canned for vulnerabilities. Every 10 to 20 seconds there is a connection attempt by a remote computer. For example, even now, when the Blaster worm epidemic is long over, there are still infected machines that try to infect others.
Update: I've just found out that aarons.cc blog was hacked.