At a conference on child safety in Edinburgh, Professor Marshall said:
"Children and young people are more likely than the rest of us to use, and to want to use, modern communications such as the internet and mobile phones and cameras. They also have a natural desire to socialise and even flirt with their peers and modern communications lend themselves nicely to that."
The Protection of Children and Prevention of Sexual Offences (Scotland) Act, which became law early this month, has no minimum age exemption against prosecution for a grooming offence.
Professor Marshall warned, however, about the difficulties of distinguishing grooming from flirting or even courting, "when it is undertaken between individuals whose age and maturity might normally lead to what most would consider to be a non-exploitative relationship".
She said: "We are going to have to be very sure of the exploitative nature of the activity before we take steps to pursue the young suspect."
Professor Marshall outlined the options in protecting children and young people:
* "We stop them from using it altogether. Now this is both impractical and unjustifiable. However I have heard of it happening in a limited way."
* "We try to regulate it from the supply side through censoring. This appears to be very difficult due to the anarchic nature of the internet and mobile phone technology."
* "We regulate it at the point of reception. This can be done by teaching young people about its dangers and about how to be discriminating consumers."
Wendy Brownlie, headteacher of Auchinraith primary in South Lanarkshire, and a member of the authority's ICT steering group, said: "Pupils need to be made aware of rather than frightened by the dangers that await them on the internet. They need to be trained about who to report to if they encounter these dangers."
Supervision was the "big one", Ms Brownlie said. "It is the responsibility of headteachers to ensure class teachers monitor internet access at all times in their classrooms."
Sexual grooming is defined in law as a perpetrator contacting a victim, who must be aged under 16, more than once for the purposes of sexual activity.
A lowering of the age barrier for the perpetrator to 16 was advocated by Barnardo's Scotland, which works with young offenders.
Bullying via text messaging was another issue discussed. Stephen Carrick-Davies, chief executive of Childnet International, said: "Cyber bullying - harassment by text messaging - is a real issue. And this is not being perpetrated by the stereotypical bogeyman."