My yahoo and facebook kena hack

Today i wake up on the morning at 10am, i suddenly cannot log in my yahoo email and facebook. After that,i getting panic, so i immediately reset my yahoo email 1st because it is important than facebook, lolz. Many of the important emails are inside this account. By reset the password, the new password will be send to the alternate email, it is very useful with an alternate email, and i dont know why the hacker never hack my alternate email as well, may be stupid? Since all my emails using the same password, i change all the password to be safe, it took about few hour to change because i need to changed the secret question and answer too,and i can't think of new password.
After that, i was thinking how do i get hack, and this is very curios because i had never encounter this problem before, i been using internet for about 12 years, i guess.. After a moment,i found the root cause of getting hack into my yahoo and facebook account. That is one of my old friend account(1st picture) in facebook suddenly comment on my photo,the comment he leave related to my yahoo secret question and answer. The comment left by the hacker is what make your first car? I did answer to his question on yesterday night. This is the clue that he used to hack my account, i dont know how he did it, but i 100% sure i kena hack because of this. Well, my old friend never leave me a comment since i added him on the facebook, lolz. So my curiosity getting stronger, i asking him on his second account, i will post the image later,please refer it...if you don't understand the image, i dont know how to explain anymore lo. His previous account have been hack too, unfortunately he can't get back his account,lol. Ok, back to topic, i immediately delete this hacker account and block his account. Right now all my 5 email accounts are change with different password and i got a problem to memorize all of them,=.=".

My advice to you guys is never ever answer the secret question and answer related to the any of the email account such as yahoo, msn, google email account and so on. Even with your closed friend also cannot answer. For example, those secret question are what is your father middle name? what make you a first car? what is your first pet name? where is your favorite food? where are you born? and etc.