How can I stop diablo ii expansion hacking?

I have heard of people getting "hacked" and losing their accounts and this has also happened to me. I am wondering:
1)how they did it?
2)how can I protect myself from it?
3)how can I do it back to them?

sounds like your more interested in knowing how to hack into things than stop it....u urself cant stop it except for changing your password...there are things that come up on some sites like....."ypu have to be logged in to do that" never log in when it says that...for example on myspace..most of the time its a trap to get your password...and for advice real advice...revenge is not the answer to things and doing that to someone else aint good ....it just get you into trouble