But with classes already wrapped for the year, some international students say they have been forced to fork out for expensive flights back to campus so they can retake the exam in time to graduate.

An ANU spokesman said the "leak", which was reported by students in the days after this month's computer science exam, had so significantly compromised its integrity that a compulsory resit was the only option.

It was highly unusual and being treated "very seriously", he said.

Students who first raised concerns in an online university forum suggested the questions had actually come from a previous year's exam said to be near identical to the 2019 test.

One student posted photos of the questions allegedly used by their friends' during revision and others quickly noted the similarities.

But an ANU spokesman said concerns that a past year's test was "recycled" had since been ruled out. The questions circulated among students appeared to have come from the current exam itself, he said, noting past tests were already published in the university library each year.

Some have claimed the questions were given to students by a private on-campus tutoring company "UP Academy", which advertises in Chinese and claims to be "officially approved" by the ANU.

It is unclear if students knew the questions would be on the 2019 test when they accessed them and the ANU said that, while the leak had been confirmed after it was "escalated promptly by student and staff", its circumstances remained unclear - including any potential link to UP Academy.

In October, the ANU's governing council mentioned the company's presence on campus at its new Kambri precinct as a "concern....that challenges efforts to promote academic integrity".

"[UP Academy] targets international students and appears to suggest that it is endorsed by the ANU," meeting minutes state.

On Thursday, students were given less than a week's notice to resit the test on November 20 - or wait until February next year.

Ma, a student in the affected "Document Analysis" course who did not want his full name published, said he was forced to cancel his own flight home to China so he could stay and resit the test on Wednesday.

"I couldn't get a refund," he said. "There's a lot of us in a similar situation. But if you wait until next year, you can't graduate. I don't know if everyone will be able to make the first resit next week. A lot have already gone home. People are furious."

Others vented their frustration in the online forum at being punished for the bad behaviour of a few.

"No way should students who didn't do anything wrong have to pay thousands of dollars for flights back to ANU and accommodation...or even spend extra time over summer studying," one student wrote.

The ANU said it regretted the inconvenience caused and those who felt disadvantaged could "follow the university's assessment appeals process".

"[We] will consider alternative exam arrangements and provide support for students affected," the spokesman said.

"If a student experiences financial hardship related to the re-sit then we would encourage they contact us individually for specific advice and support.

"[We are investigating] how this type of incident can be prevented in future."

A senior academic told students cheating would not be tolerated and the resit was considered the fairest option but promised "nobody will be expected to fly around the planet for a single exam".

This year, the federal government has drafted new laws targeting private providers who offer so called "contract cheating" services to university students.