NEWLY sober Lindsay Lohan is afraid that nude photos taken of her by British bad boy Calum Best have been stolen by a computer hacker and will wind up on the Internet.

Just weeks after sultry shots of Lohan and Vanessa Minnillo goofing around with kitchen knives hit the Web, underground site celebslam.com claims it has its hands on nude photos of Lindsay – and the stalker-ish site is threatening to publish them.

In what Web site owner “Nick” claims to be a G-mail chat between himself and Lohan, the starlet supposedly wrote: “All I know is that someone broke into my computer and left a file on my desktop saying he got the pictures Cal took from me naked.”

Regarding the photos, Lohan’s rep, Leslie Sloane Zelnik, told Page Six, “Anything is possible. I know nothing about it, but her lawyers have been contacted.”

Meanwhile, Lohan may have another headache on the horizon – a roman à clef by a Canadian author who says she tutored the star and acted as her guardian on the set of “Mean Girls” four years ago.

Andrea Dana‘s self-published “Starsitter” chronicles the rise of a bratty starlet named Maddy Malone, whose parents are on the verge of getting divorced and whose mom wanted to be a Broadway star.

In one scene, Maddy complains to her minder: “Unfortunately, I have no alcohol in here. My bitch publicist made sure of that.”

Zelnik told us, “It doesn’t work like that,” and said she wasn’t familiar with Dana or the book.

In another passage, Maddy throws a fit when she’s sent some designer clothes she thinks are too cute, bellowing: “Call [bleeping] Dior! Or I will have you off the payroll faster than you can spell it!”

Dana told Page Six: “I did go to L.A. with Lindsay, and the actual story is inspired by that trip. The character isn’t really her, but it’s loosely based . . . She wasn’t exactly a star yet, but she had the attitude like she was already a star.”

Dana also claims that at the time, Lohan was “against drugs and wasn’t going out every night and drinking, so reading about her later on kind of shocked me. It’s totally troubling as a teacher to see your student in rehab.”