No, not all bases are covered for broadband because they can still get past the modem. So you need to external firewall at the modem end.

Some modems have their own firewalls and routers.
Highly reccomended to have a firewalled Modem.

Without a firewalled modem, it's like your front and back yard has no high fence but your front door is still guarded with software firewall, and this taxes the PC.
If a hacker wants to, they can still get in through the "front door" with an "axe".
So if you have a firewalled modem,chances are they won't bother with the "front or back door".
It's a little known fact,but some advertising companies employ hackers to keep updating their spyware.