If you are cautious / paranoid about open ports in Windows, you may have noticed port 445 open.
To close it, log in as an administrator, and do the following:
1. In the run box, type "services.msc" and run the Services console
2. Scroll down to find the service "Server"
3. Right-click "Server" and select Properties
4. Stop the service, and then click the drag-down box in the center, and select Disable.
5. Restart the system.
Keep in mind that any services that depend on the Server service (e.g. Homegroups, print sharing) will fail. Consider creating a System Restore point prior to making the change.