Yep.. someone hacked in and started using my user name to buy crap on Ebay.
I found out after I had the same problem and had to request anouther password and never recieved it at my alternate email address, after 2 days I contacted Yahoo and got one.
I went to my account, closed it, and opened anouther account.
real pain to have to go everywhere online and change my address on numerous sites like MM, Bowsite,NAHC,Cabela's, Gander Mtn,ect ect ect.
You have to get anouther password from Yahoo to get back in, my spam went from <10 a day to >400 also.
close it and start again.