The percentage of U.S. youngsters aged 10 to 17 who said they were victims of cyberbullying increased from 6 percent to 9 percent from 2000-05, to a report by the University of New Hampshire's Crimes Against Children Research Center, as reported by USA Today Tuesday, said.

The report also found that the number of young people who said they had "made rude or nasty comments to someone on the Internet" increased from 14 percent to 28 percent in the same period.

But experts say many more instances of cyberbulling go unreported because of the fear that tormentors will become angrier and bully them more and the U.S. Centers for Disease Control calls it "an emerging public-health problem" that needs more attention, USA Today said.

"You're bullied twice," Nancy Willard, author of "Cyber-Safe Kids," "Cyber-Savvy Teens" and "Cyberbullying and Cyberthreats" told USA Today. "You're bullied in the real world with a physical attack, and then you're bullied online with humiliation. It's very hurtful. Very, very hurtful."