New Delhi, May 9 -- Tens of thousands of students studying for final exams around the world Friday regained access to a key online learning system after a cyberattack had earlier knocked it offline, throwing schools and universities into turmoil.

Elizabeth Polo was in a creative writing class at the University of Maryland late Thursday afternoon when a classmate shouted, "Canvas got hacked." A message from a hacking collective flashed on her computer screen.

"Our whole class just like was like freaking out about it," said Polo, a junior. "Our poor professor was trying to get everyone to calm down but it was just kind of chaos."

Across academia, the outage set off panic and confusion as students and faculty members found themselves lock...