Adultery was once kept a secret. Not online.

The Internet dating (search) craze is blazing a trail of broken marriages, thanks to dozens of sites inviting participants to identify themselves as "not so happily married," "married but that shouldn't matter" or even the seemingly archaic, "married but we swing."

Studies show some 30 percent of online dating visitors are married -- and recent research by the University of Florida (search) reports that what starts out as flirting and cybersex quickly escalates into the real thing.

The Internet became an easy escape for "Barbara," a 43-year-old married New Yorker who dated about 60 men in three years until she met Steve, who's also married -- but now sneaking around with Barbara.

"We see each other once or twice a week," she says. "We have a lot in common, have a great time together and the sex is phenomenal."

She says a cold husband sent her surfing for more. "There was no warmth or any physical affection," she says glumly.

She tried cajoling her husband into seeing a marriage counselor, but after only one visit, he refused to return. She didn't want a divorce because of their 7-year-old daughter, so she posted an ad online.

"I'm not interested in jeopardizing my marriage or anyone else's," she said. "I just wanted to find someone special I could click with."

Other women interviewed say they've been searching for deeper emotional relationships than their husbands are able to give -- but aren't ready to leave.

"I guess the sex just isn't what it used to be when we first met," says Nicole, 28, a married New Yorker who's listed her profile online. "I miss the feeling of sex being new and exciting. It's addicting."

Addiction is something that Chris Samuels, the co-director of a sexual addiction treatment center, understands all too well. She has treated many married and unmarried patients who've gotten caught up in Internet lust.

"Its power is almost trance-inducing," she says. "You can troll these sites and have a fantasy ready and waiting. Cybersex can provide a quick and powerful high. It's like crack cocaine to sex addicts."

Alfred, 49, is a self-described Internet Lothario who says he's been "swinging" for 23 years.

Before going online, he would post ads in "swinger magazines," sometimes waiting two to four months to set up a first meeting.

Now his desires can be gratified almost instantly by posting ads on the Internet.

"While I'm open to a relationship, I'd prefer someone I can meet for no-strings mutual sexual pleasure on a continuing basis," he says.

Alfred's new online ads generally attract several interested women ("I'm a seller in a buyer's market," he says proudly).

He usually hooks up with married women, but says there are plenty of singles who don't mind that he's already spoken for.

Unfortunately, while these spouses are sowing their wild oats, there's likely to be someone at home who's getting hurt.

John LaSage, 43, from California, could attest to that -- his wife left him and his two teenage daughters to take off with an Internet boyfriend.

The experience led him to create chatcheaters.com -- a Web site designed to help dissuade potential cheaters and to comfort those who've been hurt by them.

"Chatting is OK, cheating is not," says LaSage.

"People should realize how quickly relationships can form online. Flirting can lead to real-world affairs."

If you suspect your spouse of having an online affair, "Bring the issue out into the open," he says.

"Look out for the warning signs" -- like excessive Internet use, new email accounts, turning off the computer when you walk in the room.

Pepper Schwartz, a professor of sociology at the University of Washington and the relationships expert for online dating site Perfectmatch.com, says married men are much more likely to say they're just looking for sex than married women, but ultimately the search is about loneliness.

"... It's about gratification," she said. "They want someone to find them attractive, someone to want them passionately."

But not every married person who's gone the online route has found the affair of their dreams.

Wayne, a 49-year-old man from New Jersey, complains that his inbox is usually cluttered with undesirable partners and a fair share of transsexuals and cross-dressers.

But that may be just the ticket for 34-year-old "Rockerdude" of New York City, who advertises online that he's hoping to make sweet music with men, women -- and anything in between.

"Yes, I am married, but we have a very liberal, open-minded relationship," he writes.

With additional reporting by Michael Shashoua