Attack to my old Email account

My old email account is compromised. I haven’t been used my old account for a long time. It is my first time since I started using computer many years ago.
My husband told me that he received strange email from me and it seemed that my email account was hacked. If he didn’t tell me about this, probably I would have not known it had happened. Fortunately it was not my current account but I changed my password of all sites. The old password had 11 characters include numbers and symbols. I realized no passwords are safe when cunning smart hackers decided to attack.
I often heard that we needed to change password often. I haven’t changed my password for a long time. There are several website about how often change the password. I like answer from the wiseGEEk:
http://www.wisegeek.com/how-often-should-i-change-my-password.htm
I like to prevent being attacked again. My decision is to change password every 4 month and select strong password. I set my calendar reminder to do so.