"It seems that an attempt was made to change the marks of some students," he said on Tuesday.
But he said there was never any danger that UQ would admit students on the basis of falsified records, because the computer system that was targeted wasn't the one used to compile final results statements for pupils.
Industry sources told AAP the results of 30 to 40 students were manipulated and the incident bore the hallmarks of an orchestrated hack.
The college won't say how many records were changed, just that it's less than 30 and only "some" were affected.
"From our point of view our quality assurance worked," Mr van Balveren said, adding UQ was informed immediately.
Sources associated with IES, who don't want to be named, told AAP that student results continued to be changed even after "the first whiff of problems", and that some staff cross-checking results had watched numbers change in real time.
In some cases, academic results had been manipulated upwards by just a few percentage points, to reach benchmarks set by UQ, in other cases students marks had more than doubled.
Queensland Police confirmed in a statement it received a complaint from IES on November 30 regarding an alleged computer hacking or misuse incident, but said it was "inappropriate" to comment until the investigation was finalised.
UQ trusts IES College to run a foundation year programme for foreign students hoping to enter undergraduate courses.
They pay between about A$23,000 and A$30,000 and if they hit UQ's benchmark results they are guaranteed a place in the course of their choice.
Prime Minister Malcolm Turnbull recently said his government took "very seriously" media reports the Chinese Communist Party had attempted to influence Australian media, universities and politics.