A computer security breach at a health insurance company was responsible for an identity theft at UC Irvine that affected 1,132 students, and led to fake tax returns filed for at least 155 of them, officials said Thursday.

A criminal investigation is under way in the case, which came from a leak at Minnesota-based UnitedHealthcare, the insurance provider for UCI graduate students.

“They have made no arrests,” campus spokeswoman Cathy Lawhon said.