Released on the eve of Valentine's Day, the survey of 1,000 people commissioned by marketing consultant Euro RSCG Worldwide found one in five said they have had a romantic or sexual relationship start online. Forty-nine percent knew someone whose relationship began that way.

Conversely, one-third of respondents surveyed earlier this month knew someone whose relationship ended because of online actions, and three-quarters believed strongly sexual communications conducted online outside of a relationship constituted cheating.

Online romance has evolved from the early days of flirting in a chat room or "cybersex" between strangers who had no intention of meeting in person.

"What people did online stayed online, for the most part," Euro RSCG Chicago Group President Norm Yustin said. "Now our two worlds are blended, and the people we meet online and how we behave on social networks is affecting us at home and at work -- for good or bad."

Deception is a constant online risk, and two university communications professors found in their research that 80 percent of the 78 profiles they sampled from matchmaking websites strayed from the truth to some extent.

The professors identified helpful clues as to who might be stretching, or shrinking, the truth about themselves: Liars tended to avoid the first-person pronoun "I" to distance themselves from their lies, they frequently employed negation such as "not boring" rather than "exciting," and they kept their self-assessments brief.

"The less they write, the fewer untrue things they may have to remember and support later," said Catalina Toma of the University of Wisconsin-Madison, who teamed with Jeffrey Hancock of Cornell University.

Weight was lied about most often, with women off by an average of 8.5 pounds (3.9 kg) and men by 1.5 pounds (0.7 kg). Half fudged their height and one in five lied about their age.

"Someday there may be software to tell you how likely it is that the cute person whose profile you're looking at is lying to you, or even that someone is being deceptive in an e-mail," Toma said. "But that may take a while."

(Editing by Daniel Trotta)

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