Terrorist groups lurk on social networks like Facebook and YouTube to entice people to join their movement, a new study warns.

The study, conducted by Australian Strategic Policy Institute, recommends limiting of extremist campaigns online by Australian authorities and their international counterparts.

ASPI's security program director, Dr. Carl Ungerer, says terrorist Web sites have evolved with the advancement of Internet technology and the terrorists are now operating more sophisticated encrypted sites for their programs to radicalize prospective recruits by communicating with them in their own languages.

Social networking sites are widely used by terrorist groups and supporters to incite violence and to connect instantly to wider audiences, he said.

Ungerer says there are now more than 5,000 active terrorist websites worldwide, many of which are operating from the U.S., where free speech is constitutionally protected.

Ungerer said the Federal Bureau of Investigation has found the terror groups are radicalising children as young as 14 years old.

While Australia and other nations had introduced new policies to counter terror activities online, only an internationally uniform legislative control can prevent online material being used for radicalisation, Ungerer said.