It has been happening for a while. I’ve been having a lot of spams which seem to come from my friends’ email accounts with their names and signatures. Check this out:
Sender address isn’t fake. They (spammers) are really hacking your email account and logging in. Then sending this type of emails to the all of your contacts!
Unfortunately, my account has been hacked and I faced up to the same issue. Have a look at what I came across in my logging activity:
It is that clear! Someone from Croatia sending those spams from your account! Here is the official help page of Yahoo for this issue. You should go through all the steps and make sure your account is safe.