Scenario:
Someone shares a couple of folders on their network, and they connects their macxhine to the Internet. Now their port 20 will be open, and everyone who feels a need for it (by any reason) can enter their shares as a normal network user.

Now, if u add a password to your shares, then it might get a bit tricky.

But Ive got this wannabe |337 friend, who claims that he can acsess my comp (with passworded shares), using the port 20 backdoor. And he says that he's able to mess around on my whole comp, after gaining acsess trough port 20.

Questions:
1. How do he bypass the network password?
2. How do he gain acsess to the whole comp?
3. How do I prevent him from doing so?
4. How's the differences between 98/2000/XP?