My girlfriends parents want to claim me as a tax exemption.?

I'm living with my girlfriends parents. and paying them 100 dollars every other week for living expenses. They are filing their tax returns and the lady that is doing their taxes say they can claim me as an exemption, but not a dependant. I've looked on the IRS website, as well as google, but can't seem to find any information regarding claiming this kind of exemption on a non-relative. I don't want to release my SSN to them to fill this out without knowing for sure its a legal move and won't have any negative bearing on me. They have ured me they are not claiming me as a dependant as I have already filed independantly. I do not meet the criteria to be claimed as a dependant. Does anybody know what exactly a tax exemption on a return is and how it would apply to me?