The initial online threat had been revealed during the routine monitoring of websites sparked by threats made against three universities last month.
"Police take all threats of this nature seriously and investigations are continuing to ascertain the identity of the person who made the threat," Inspector Thompson said.
Mr Kersten said the initial online threat that was levelled at the school a few weeks ago was the first he had faced during his career and the college was once again working closely with police.
"We're just working with the police and we are maintaining vigilance and security - they are there for us and we are on our own account as well," he said. "We have enhanced security and we're trying to operate as normally as we can because we've got MTA examinations in progress and we've got regular school as well."
He said the Rathkeale College parent community had been "fully informed about what's going on and the information we have and we're working with police to be as normal and consistent as we can while maintaining absolute and total vigilance on activity in and around the school".
"We're trying to carry on as normal. The police have been advised and are involved and are fully supportive of what we're doing."
Mr Kersten said the operation of classes and college sporting activities was unaffected and extra security personnel had been posted at the school as well.
The Hadlow School senior cricket team had been due to play a match at the college yesterday but parents were told the game there was canned and an alternative venue sought, as "due to the threat we have decided it would be unsafe".
Inspector Thompson said that despite the "recent spate of hoax threats to educational institutions", police urged people to immediately report anything suspicious or out of the ordinary by calling 111.