The new computer science GCSE has been thrown into disarray after programming tasks worth a fifth of the total marks were leaked repeatedly online.
Exams regulator Ofqual plans to pull this chunk of the qualification from the overall marks as it has been seen by thousands of people.
Ofqual said the non-exam assessment may have been leaked by teachers as well as students who had completed the task.
The breach affects two year groups. The first will sit the exam in summer 2018.
Last year 70,000 students were entered for computer science GCSE.
A quick internet search reveals numerous posts about the the non-exam assessment, with questions and potential answers.
There are even posts from one of the exam boards reminding students that they are monitoring certain websites.
A statement from the regulator said: “Non-exam assessment in computer science is intended to test students’ programming skills and is worth 20% of the overall nine to one grade.
“However, there is evidence that some of this year’s tasks have been posted to online forums and collaborative programming sites, contrary to exam board rules.
“Detailed solutions have been provided in many cases, and some of these posts have been viewed thousands of times.”
This is against the rules and changes would be needed so grades could be awarded fairly next summer, Ofqual added.
The regulator is running a short consultation on how to proceed.
Its preferred option would keep the non-exam assessment task, but to change it so it no longer contributes to the overall mark.
Julie Swan, executive director for general qualifications, said: “It is with great reluctance that we are proposing to change a qualification for which students are already studying.
“However, we must take immediate action to address these issues and the potential impact on public confidence in relation to this qualification.
“Subject to the consultation responses, we believe our preferred solution will deliver fairer and more reliable results than would otherwise be the case.
“It will also allow us to be confident that standards will be set appropriately.”
Geoff Barton, of the Association of School and College Leaders, said the integrity of the assessment had been compromised by the “widespread availability of solutions online”.
He added that of all the subjects, computer science was the one where students were most likely to be aware of “online opportunities”.
“It is an enormously frustrating situation for all concerned but we recognise that Ofqual has no option other than to consult on alternative arrangements,” he said.
He added that other options would be needed in the longer term as “the ubiquity of online information” made this form of assessment extremely vulnerable.