Your facebook account has a hacker script in it. usually it is put in by whoever edits it and sets it up un-knowingly.
Alot of "**** my profile" type sites that give you cool backgrounds, or other add-ons include scripts in the code that send emails to all your contacts without you knowning it, until someone tells you about it. They are meant to advertise random sites (Usually sites that paid for advertising from a company that promises massive amounts of traffic to there sites)
The best thing to do is clear any and all add-ons, and backgrounds, pictures/images you picked up from other sites or facebook users, and tell your friends not to open those emails as well. Then run a virus scan on your computer, Malwarebytes Virus Scanner seems to be the best out there for free, easily rivals the top VS programs that actually work that cost $300+ a month.
You can get Malwarebytes free here: http://download.cnet.com/Malwarebytes-Anti-Malware/3000-8022_4-10804572.html
Then contact the Facebook Customer Service and tell them about it, They can run a scan on your profile and make sure there is no scripts on it, as well as remove anything they do find.
also, don\'t forget to change your passwords ASAP, including any passwords to any sites you have personal information on, such as ebay, paypal, your online bank, etc... Its good to change your passwords often on anything that has information pertaining to your finances, or about you.
Goodluck with your profile.