Peculiar situation

If that happened to me I would immediately change my password.

 

You were hacked. You need to close the account and open a new one with a different password. Delete any personal information from your emails and pray nothing was stolen.

 

And always put numbers in your password and use a misspelling of a word.. Do not make the password short. Be sure it is at least 7 characters long. I read somewhere that something like 30% of all people use the word password as their password.

 

I wouldn't delete the account, but I would definitely change the password and all other security measures it has (I don't remember off the top of my head all that yahoo uses). If ANYTHING has been changed, contact Yahoo and let them know immediately. They can prevent anything untoward befalling the account. If you are like me you have used the account for quite a while and losing it is not an option.

I don't remember how I finally did it, but you can set Yahoo to not use the chat automatically. I use Trillian as my IM client (it handles several different clients at one time), so logging in via my email was redundant. Besides, if I want to chat I want to make the decision to open up a client... not have it forced on me.

Again, change your security (passwords, questions, everything), make sure you have another email account that security updates will be sent to should the password change (such as a Gmail account), and let Yahoo know if ANYTHING has been tampered with.

Crabtownboy's suggestion is a very good one. A great trick is to use a short phrase, but substitute some "leet" in it. "Leet", or 1337, is substituting numbers for letters, like 3 for E of 4 for A or 7 for T or 1 for L. Get it? I once used h0t3lc4lif0rni4 as a password... but it was a real pain for me to slow down to type it.