Secret Internet Formulas for Determining Sexual Orientation

I have a profile on Facebook.com, and it's been up for almost three years now. Being the secretive, private type who's not really shameless at all, I've never specified which gender I'm "interested in" on the site - though I have signified that I'm interested in "random play."

However, in recent months, Facebook has begun hosting more ads than ever, and I've noticed something peculiar happening. Many of the ads that appear in my sidebar have pictures of shirtless men, and say things like, "Curious about Men for Men?" And so far, I've yet to see any ads with women in them when I log in. Facebook has somehow concluded that I probably am interested in men, and tailored their ads to me in that way. But the unsettling thing is that my profile doesn't say this anywhere, meaning that the site must have a formula for determining sexual orientation beyond what the user chooses for their "interested in" category. Whether its based on interests, or maybe even things like declining to specify orientation, Facebook is making a judgment. This is the kind of thing that's probably going to become more common as the internet becomes even more saturated with ads and sites like Facebook become more interested in selling users' information to advertisers.