Operators of the ACT college entrance exam have canceled the tests for students in South Korea and Hong Kong at the last moment over what they said was a verified breach of test materials.

ACT spokesman Edward Colby said Saturday the cancellation affected about 5,500 test takers who will receive refunds of test fees.

Colby says that the exams will be administrated in South Korea and Hong Kong again in September.

South Korea has struggled to clamp down on cheating on standardized English and college admission tests and similar problems have been reported in China.