Tess Lippincott has seen the writing on the wall.

She deleted it.

That's because the writing came from her mother. And it was in direct violation of the rules that Tess, 16, had set up when she allowed her mom to become her "friend" on Facebook, the networking site once dominated by teens and twentysomethings and now growing in popularity with older folks.

Her mother, Jenifer Lippincott, who happens to be a parenting expert and author of "7 Things Your Teenager Won't Tell You (And How to Talk About Them Anyway)", knew the rule about not posting on the wall; she's also forbidden from friending her kids' friends. She understood the rules and agreed to them. But she just "couldn't resist" and posted her favorite "IM/e-mail comment: umamaluvsu" on Tess' wall.

Tess deleted it as soon as she saw it. "I definitely don't want her to be posting on my wall and having all my friends being like "Is that your mom?' It's weird," says Tess, 16, of Washington, D.C. "It may have been up overnight, but hopefully not that many people saw it."

Just a year ago, teens and twentysomethings pretty much had Facebook, along with other social networks, all to themselves.

But Facebook didn't just seem exclusive, it really was.

When Mark Zuckerberg and co-founders Dustin Moskovitz and Chris Hughes launched the site from their Harvard dorm room in 2004, it allowed only users with campus e-mail addresses, creating, in effect, a gated country club for the college community.

Soon, students around the country began sharing stories, pictures and gossip with each other as if they were sitting on the campus quad.

In September 2005, Facebook opened its doors to high-schoolers, then in September 2006, to all comers - and coming they are.

That month, about 75,000 active users on the site were 35 or older, accounting for fewer than 1 percent of all active users, according to data provided by Facebook. By August 2007, the number shot up 4,700 percent to 3.6 million active users 35 and older. That accounts for about 9 percent of active users.

Living in the world without the usual social barriers between generations is causing a little discomfort for some and downright angst for others.

"Think about what it would be like if your mom or dad enrolled in your high school class," says Steve Jones, communications professor at the University of Illinois, Chicago. "They don't belong there. That's the same feeling (children) have: "This is ours. This belongs to me. This is not for parents.' "

The generation that grew up with the Internet has "this sense of "This is not something you'll ever get. You won't understand what we're doing. You're going to ruin it. We'll never be ourselves if there is an adult around here.' "

CROSSING THE TECHNOLOGY GAP

Teens, like adults, have a range of reactions to their parents being online, says Anastasia Goodstein, author of "Totally Wired: What Teens And Tweens Are Really Doing Online".

"Some teens are perfectly fine with that and welcome their parents' presence," she says. "Other teens are fiercely protective of their privacy, and they see it as their private space."

Even teens who say they're happy Mom and Dad are joining the social-networking party have had to deal with the technological generation gap.

Kids grew up with Internet-speak and understand Internet culture as natives. Parents, on the other hand, are foreigners, and that's often obvious.

Laura Benson, 17, of Huntington, W.Va., says she lets her mother see everything; they have a close relationship, and she has nothing to hide. But she still is sometimes embarrassed by her mom's Facebook faux pas.

Take the time when her mother, Connie Benson, 50, got upset about a rude comment, including the f-bomb, someone had posted underneath a photo her mother had taken. (Most kids will tell you foul language is just part of the Internet culture.)

Laura advised her mother to ignore - and delete.

Her mom did delete it, but she hardly ignored it. She sent the offender a note and said, "I don't want to have any curse words on my site," Connie Benson says.

She understood her daughter's request but felt compelled.

"As an adult and a Christian woman, I just feel like I need to confront these kids," Benson says. "Since it was in my face, I needed to address it."

Laura was exasperated. "I was like, "Why don't you just delete it? Don't do that anymore. Let it go.' "

Tess says her mom's wall post was "like if I'm having a bunch of friends over, and my mom came down and started striking up a conversation with everyone, or saying, with all my friends over, "Oh I love you so much' and giving me a hug and kissing me all over."

Tess actually likes her mom being online; in fact, she helped build the profile for her mom, who uses the site to do her own social and professional networking as well as to communicate with her children.

Still, Tess says, "older people being on Facebook is kind of weird."

But is it weird enough to turn young people away?

Some speculate that as parents and other adults increasingly invade these online spaces, "young people are going to move on," says Amanda Lenhart of the Pew Internet & American Life Project, which studies how people use the Internet.

Facebook, however, like many social networks, including online leader MySpace, is going through a massive growth spurt - not just with older folks, but with everyone. Facebook now boasts 43 million active users.

A SECRET PLACE OF THEIR OWN

It's hard to know when people turn elsewhere because they often maintain their current social networking profiles while seeking out other sites, Lenhart says.

Kids also are likely to "demand tools that will allow them to be different in a private space than in a public space."

Facebook already allows users to selectively hide parts of their profile from others, so a friend may be able to see who you're dating and what you did at that party, but your parents would be blocked.

How well parents and teenagers get along online and how far kids let their parents in can depend on many factors, including the child's age and the parents' behavior.

But "to me, it all goes back to what kind of relationship do you have with your kid," Lippincott says.

Some teenagers clearly resent parents' presence on their site.

One facebook group is called "At Least MY Mom Isn't On Facebook!" Another is dubbed, "Against Parents Invading Your Facebook (YES MOM THAT MEANS YOU!)"

One teen who was a member of that group, who was contacted by USA TODAY on Facebook, says her relationship with her parents is so bad that she not only locks her bedroom door, she also blocks her mother from being able to see her online profile.

Facebook, says Hannah Cobb, 22, a student at Florida State University whose mom has yet to join, "was almost like a secret community for college kids where you could put up all your pictures from your nights out partying, and no one would ever see them except for your friends. Now it's more like a lot of the school administrators are on there - professors and stuff - and they can see what you're doing.

"And now your parents are on there. They can see what you're doing, too. Not that I personally have anything to hide. I don't drink or party or anything at all. But a lot of my friends were a little freaked out when their parents joined."

Her one wall post notwithstanding, Lippincott says she abides by the rules. "You are not your kid's friend," she says. "You are your kid's parent."

Parents who have access should use it wisely, Lippincott advises.

"Going on to Facebook and checking out your children's profile is really not much different than going into your kid's room or looking through your kid's things."

There definitely are times when that's appropriate, she says, especially with younger teens.

But "you have to be respectful. This is a domain that is theirs."