Hayden Panettiere has been a bad, bad girl.

Seriously, you're not going to believe what naughty things the Heroes star has been up to. According to sources, Hayden Panettiere, 18, recently reduced her mother, Leslie Panettiere, to tears when she got a tattoo without her parents' permission.

The sexy Heroes cheerleader actually got the tattoo done a year ago, and managed to keep it a secret from her protective parents for a time.

"It's a small Leo symbol [her zodiac sign] on my ankle. My mom didn't see it for ages," says Hayden Panettiere of her clandestine tat.

The lovely lady's tattoo didn't remain a secret for all that long, though, as a hot new acting job intervened, forcing Hayden Panettiere to out the hidden body art.

"I was being body-scanned for a special effect on Heroes," Hayden said. "And she saw it, then tried to rub it off, and suddenly I realized. Her eyes welled up."

Hey, could be worse. What would Hayden's parents think if they walked in on their daughter having ... an even bigger tattoo inked on her petite frame? Or multiple tattoos!?

Or, what if there were Hayden Panettiere nude pictures floating around! My goodness. Imagine the kind of uproar that would cause on the home front.