Cable modem needs a router

If you are using a cable modem you need to connect it
to a router instead of directly to your computer.

If you do not have the router, then you need to make sure your
computer's firewall is turned on and file and print sharing is
turned off. Without your own router, it is like connecting in
an airport or hotel. Your computer is safe if you follow these
precautions.

Internet ------ Cable Modem ----- Your Router ---- Your Computer
Firewall Firewall

A router cost about $50 and is set up with a firewall automatically.
You then have a secure network in your house. You can connect other
computers (if you have a visitor). You can safely use file and print
sharing.

In either case, you do not need anti-virus software, as Windows
comes with a firewall.