Firsly, didn't your teachers tell you that the only stupid question is the one you didn't ask?

You would have felt worse not asking so don't worry about it, this is what forums are for.
and to answer your question...
Any internet connection is open to virus',
Any network connection is open to virus',
A CD/DVD burnt by a mate, is open to a virus.
etc,etc,etc.
If you have a computer and you connect it to other computers (this is what you are doing) or you use a disk that has been in another computer (or a memory/usb stick/pen drive) then you are open to a virus.
This is why it is nessesary to keep your computer up to date with service packs, updates, antivirus, firewalls and spyware protection.
Your computer is connected to your neighbors and his/hers is connected to yours, and so is mine (via the internet). We are all open to virus.
I'm not trying to scare you, but you need to be protected, there are good freeware AntiVirus' out there I can mention some but I'm not sure if it would be considered "naughty" by the forum moderators.
do a google for "freeware antivirus" the first couple are both good, my preference is number two, but others would prefer number 1 (not counting sponsored links)
Enjoy your connection, well done