Boston: A study has revealed that social networking site Facebook has 7.5 million underage users who are not supposed to use the website.

Of the 20 million minors who actively used Facebook in the past year, more than one-third or about 7.5 million were younger than 13 and not supposed to be able to use the site,
Consumer Reports, an American consumer advocacy publication, said in a study.

Among the young users, more than five million were 10 years and under, whose accounts were largely unsupervised by their parents. One million children were harassed, threatened and subjected to cyberbullying on the site in the past year.

The study said majority of parents of 10-year olds and younger kids were "largely unconcerned" about their child using the site.

"Despite Facebook's age requirements, many kids are using the site who should not be," Consumer Reports technology editor Jeff Fox said in the statement.

"What is even more troubling was that a majority of parents of kids 10 and under seemed largely unconcerned by their children's use of the site."

Facebook, which has over 500 million users, screens applicants by asking for their birth date and rejecting those too young.

However, a pre-teenager can join the network by falsifying his or her birth date. Further, since joining Facebook does not require a credit card, it is easier to give incorrect information to join the network.

The report said parents of 10 year olds and younger kids on Facebook seem to be largely unconcerned. Only 18 per cent made their child a Facebook friend, which is the best way to
monitor the child. Only 10 per cent of parents of kids 10 and under had frank talks about appropriate online behaviour and threats.

"Parents think their young children are less likely to take risks online and their younger kids are not interested in porn. With a 10-year-old mentality, they are only interested in 10-year-old things," says Vanessa Van Petten, creator of blog Radical Parenting.