Hi everybody:
I've a cablemodem Thomson vcm 770. The isp, gived it to my like a cablemodem, so i can get 3 different public IP's for my machines, but that is the maximun.
I'm wondering if this is real secure or not, because the cablemodem is in transparent mode, so i think nobody can attack it from internet... but the question is... is that really? Anybody could make a Mitm? Am i secure? Can the machine which is connected be attacked?
Thx for all friends... Im just a newbie here!

If you're not running public services on your computer I wouldn't put public IPs on them. Even if you were running public services on those computers I'd use some sort of PAT or NAT with ACLs. All these things are standard in home routers. It's always best to network computers behind some sort of dedicated firewall and deny all by default and only open up what you need.

You wouldn't want to learn by setting your box up on the Internet. While you are trying to figure out what to do, the bad guys will be pillaging your personal information. Use a private network and learn from there. As far as what attacks are possible, it depends on what services are running on your computer.

What operating system are you running?