Email Hackers

Hey. Here’s a question for those of you who know a little about hacking. I have a friend who keeps getting her yahoo account hacked. She changes the password, but they get it every time, and occasionally just use her account. Now I’m trying to figure out how someone could do that, unless they had a trojan or something on her computer. I mean surely it’s not that easy to continually hack someones yahoo account is it? I know very little about hacking, so any ideas would help.