Some time ago, I installed a router/firewall at my parents' place in San Diego County. Naturally, none of the machines behind the firewall are protected because... well, because there is a firewall (duh). When our old DSL provider shut down, my dad signed up for new DSL service and (unbeknownst to me) disconnected the god-damned firewall to install the software that came with the new service. My mom has been complaining about the speed of the machine ever since. I didn't know what was wrong until I went in to check the machine out via VNC this evening ("Dad -- can you install VNC? Here's the URL. Make sure you install the server.")
It turns out that some immature bastards have been having a field day with the machine ever since the firewall was disconnected. Just about every backdoor on the planet has been installed, including keystroke loggers -- and who knows what else. I told my parents to assume every file on the machine had been compromised, which unforunately means that they will have to do some work to change passwords, account numbers, etc. Norton Antivirus hasn't been helping much since it for some reason doesn't have "access" to delete or move the offending files in Windows 2000, so I had to track down specific remover executables for each of the worms that I discovered (by doing google searches on strange files that I found in the file system). It's been more than 2.5 hours so far, but I think I'm almost done "cleaning."
A summary, for those of you who are still having problems understanding what happened (heh):
1) router installed. everyone is happy.
2) dad uninstalls router. someone sticks worm(s) in startup folder.
3) parents reboot computer. all hell breaks loose.
4) parents complain to eric. eric vnc's in to see what is going on.
5) eric spends 3 hours removing worms and viruses. almost 4000 files infected.
This kind of shit must go on all the time. All you have to do is buy a new computer, sign up for DSL, plug your machine into the DSL modem, and suddenly your machine is connected to the entire world. You had better know what you are doing.
I should limit admin access to my parents' machine so I am the only one who can change anything; it might help to lower my blood pressure.
*update* - So, if you have your machine plugged directly into your DSL/Cable modem and are wondering how to secure it from hacking, try this (Windows XP only):
1) Click on your desktop and hit F1 to bring up the Help and Support Center. Do a search for "firewall" and click on "Enable or disable Internet Connection firewall." Follow instructions to enable Internet Connection firewall.
2) Then, double-click on "My Computer" or "My Documents" on your desktop and select Tools->Folder Options from the menu in the window that pops up. Click on the "View" tab and scroll down to the bottom of the "Advanced settings:" box. Make sure "Use simple file sharing (Recommended)" is checked. Once you check that box, only files in the "Shared Documents" folder will be shared with the rest of the world. :)
Good luck. :)