Like most teenage girls, Hannah and Mackenzie love to check their Facebook accounts or post photos. But, one day, one of Hannah's friends was brutally attacked online.
"They were making up rumors about her, calling her a whore, saying she was ugly and she wasn't pretty, and no one should like her and no one does like her," Hannah said.
"Here, this beautiful, smart, intelligent, well-rounded young girl was being just sexually harassed and taunted at every turn," Hannah's father, Sam Black, said.
In addition to being Hannah's dad, Black is an Internet safety professional. He knows first-hand what dangers lurk online for teen girls, including his daughter. "Body image, sexualization of women and girls, cyber bullying - all these things can play out on the Internet."
"There are a number of new sites that look like they're harmless, but are actually teaching our girls very, very vicious lifestyle changes," said Michele Borba, Ed D, the author of "The Big Book of Parenting."
Borba just released her list of top offenders, which includes the site where Hannah's friend was bullied. "Formspring is one of the new kinds of websites that looks like a social network that is popping up online for our daughters. It looks tame enough, but once they log on, what it actually encourages instead, is to send vicious notes toward one another in an anonymous nature."
"What it really ends up doing is exposing the girl to sexual taunts, derogatory language, just nastiness that you could never imagine," Black added.
Formspring refused our request for an on camera interview, but in an email told us it takes safety and privacy very seriously and has developed practices for blocking inappropriate content.
That's not the only website that concerns Borba and Black. New online games where teens create and play highly-sexualized characters are a shock.
"For example, one is called the bimbo game. Breast implants, and if you earn a certain amount of points in life, you can even buy yourself a sugar daddy," Borba said. "Totally unhealthy, and you do not want your daughters in any part of it."
"These kinds of games only demean what girls think about themselves," Black emphasized.
Then there are the websites that promote unhealthy lifestyle choices, such an anorexia and bulimia, with photographs of super-skinny models and step-by-step tutorials.
"Specific directions on how to purge, how to purchase diet pills, and it is doing damage. Stanford University found that 96 percent of girls who are anorexic learned a lot of their eating habits on those sites," Borba charged.
So how do parents keep their teens off these websites? Our experts say the first step is to invest in parental control software, monitor your teen's online history.
Also do Google searches on their full names to see if anything comes up and limit their time online.
"If they have a limited time on the Internet, they'll be more wise about what they do online," Black said.
Take the time to get Internet savvy yourself. It could make all the difference in your daughter's life. "You need to step up to the plate, you need to monitor because we're raising our children in a tough world," Borba said.
As for Hannah and Mackenzie, they say they have no time for Internet bullies and neither should their friends.
"You should just ignore it and go with what your best friends tell you. Keep yourself up high," Mackenzie said.
The makers of the bimbo game say the average age of their users is 19 and insist their players know the difference between a game and reality.
That said, don't wait too long to talk to your kids. A national survey found 85 percent of 12 and 13 year olds have experience with cyber bullying, with 53 percent saying they have been bullied online.