I have a firewalled router, does that help?
And don't viruses run as a file and then you see them when u do Ctrl+Alt+Del?
I always check that and I've never seen anything weird, checked it on www.tasklist.org etc.
Q~
Sadly, that's not the way it works. While simple viruses might show up there, anything advanced will know how to hide itself.
We're talking about 2 things now:
Viruses/Worms
Exploits over the network
For the first issue, only a antivirus application will help, or if you're 100% sure nothing dangerous is ever executed (you'll never be).
For the latter your router does help, and this is what the thread starter was talking about. If you configured port-forwarding on your router, keep the ports required to a absolute minimum! Otherwise you circumvent the protection your router is giving you.
Ok, here's the interesting stuff. You can run an online portscan from a trusted source. Be warned that this can give you serious (temporary) issues while the scan is running. I will not give you a direct link to such a service, as you can easily google for one and decide whom you trust to do so.
This will show you which ports might be an issue and can be connected to directly from the internet.