Southern Illinois University says an apparent breach of one of its old computers in Carbondale may put about 900 students at risk of being defrauded.
Someone may have accessed a mathematics department computer that apparently had the names of students from about five years ago, school spokesman Rod Sievers said.
Social security numbers were still used then as student identification numbers.
Sievers says letters have been sent to as many students as the university could find, warning them of the breach and advising them to put fraud alerts on their accounts.
The letter asks anyone who might be a victim of fraud because of the breach to contact police and credit bureaus.